                                               Filed:   June 26, 2012

                   UNITED STATES COURT OF APPEALS
                       FOR THE FOURTH CIRCUIT


                            No. 10-4133
                     (5:06-cr-00024-RLV-DSC-1)


UNITED STATES OF AMERICA,

                Plaintiff - Appellee,

           v.

SEAN C. SOWARDS,

                Defendant - Appellant.



                               O R D E R


           The Court amends its opinion filed June 26, 2012, as

follows:

           On page 33, section II.B., second line of text, and on

page 46, section III.D., third line of text -- the word “than”

is corrected to read “that.”

                                        For the Court – By Direction


                                            /s/ Patricia S. Connor
                                                      Clerk
                       PUBLISHED


UNITED STATES COURT OF APPEALS
             FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,             
                Plaintiff-Appellee,
               v.                          No. 10-4133
SEAN C. SOWARDS,
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
 for the Western District of North Carolina, at Statesville.
          Richard L. Voorhees, District Judge.
               (5:06-cr-00024-RLV-DSC-1)

                Argued: December 9, 2011

                  Decided: June 26, 2012

          Before TRAXLER, Chief Judge, and
         GREGORY and WYNN, Circuit Judges.



Reversed and remanded by published opinion. Judge Wynn
wrote the majority opinion, in which Judge Gregory con-
curred. Chief Judge Traxler wrote a dissenting opinion.


                        COUNSEL

ARGUED: C. Dennis Gibson, II, DENNIS GIBSON LAW,
PLLC, Ridgecrest, North Carolina, for Appellant. Melissa
Louise Rikard, OFFICE OF THE UNITED STATES
2                  UNITED STATES v. SOWARDS
ATTORNEY, Charlotte, North Carolina, for Appellee. ON
BRIEF: Anne M. Tompkins, United States Attorney, Char-
lotte, North Carolina, for Appellee.


                          OPINION

WYNN, Circuit Judge:

   On appeal, Sean C. Sowards argues that the district court
erred in denying his motion to suppress because the police
lacked probable cause to initiate a traffic stop based exclu-
sively on an officer’s visual estimate—uncorroborated by
radar or pacing and unsupported by any other indicia of
reliability—that Sowards’s vehicle was traveling 75 miles per
hour ("mph") in a 70-mph zone. We agree and therefore
reverse the district court.

                               I.

   Deputy James Elliott stopped Sowards for speeding along
North Carolina’s Interstate 77 after visually estimating that
Sowards’s vehicle was traveling 75 mph in a 70-mph zone.
Although Deputy Elliott’s patrol car was equipped with radar,
he had intentionally positioned his patrol car at an angle that
rendered an accurate radar reading impossible. During the
traffic stop, Deputy Elliott had a canine trained in drug detec-
tion, Ringo, sniff the outside of Sowards’s vehicle. When
Ringo signaled the possible presence of a controlled sub-
stance, Deputy Elliott, along with other officers, searched
Sowards’s vehicle and discovered approximately 10 kilo-
grams of cocaine. Subsequently, a grand jury charged Sow-
ards with possession of at least 5 kilograms of cocaine with
intent to distribute, in violation of 21 U.S.C. §§ 841(a)(1),
(b)(1)(A).

    Before trial, Sowards moved to suppress the evidence on
                        UNITED STATES v. SOWARDS                               3
the basis that Deputy Elliott lacked probable cause to initiate
the traffic stop in violation of the Fourth Amendment.1 At the
suppression hearing, Deputy Elliott testified that he was certi-
fied in the use of radar equipment in North Carolina. As a
condition of obtaining radar certification, Deputy Elliott was
required to visually estimate the speed of twelve separate
vehicles and then have his visual speed estimates verified
with radar. To pass the road test, Deputy Elliott’s visual speed
estimates could not vary from the radar by greater than a total
of 42-mph for all twelve vehicles combined. Deputy Elliott
testified, however, that, for any one vehicle, his visual speed
estimate could have been off by as much as 12 mph, so long
as he did not exceed the 42 mph total for all twelve vehicles
combined.

   Over the objection of defense counsel, Deputy Elliott testi-
fied that he had visually estimated that Sowards’s vehicle was
traveling 75 mph. Deputy Elliott further testified that the
posted speed limit was 70 mph and that, therefore, Sowards’s
vehicle was exceeding the legal speed limit by 5 mph. Deputy
Elliott also stated that he did not attempt to verify, or other-
wise corroborate, his visual speed estimate with his radar unit;
he did not attempt to pace Sowards’s vehicle with his patrol
car to gauge the speed; and he had not been trained on, and
therefore did not use, the VASCAR system, which utilizes a
stopwatch to approximate the time it takes a vehicle to travel
over a predetermined distance.

  When asked what technique, if any, he used to estimate the
speed of Sowards’s vehicle, Deputy Elliott testified as fol-
lows:
  1
    Sowards also challenged, among other things, the open-air dog sniff on
the basis that the officers lacked the necessary reasonable suspicion that
illegal activity was afoot to continue his detention beyond the time
required to issue a traffic citation. Because our disposition rests on Deputy
Elliott’s lack of probable cause to initiate the traffic stop in the first place,
we need not reach these issues and have, accordingly, omitted the related
facts.
4                UNITED STATES v. SOWARDS
    Q. [Government counsel] And do you learn certain
    techniques in visually determining the speed of the
    vehicle?

    A. [Deputy Elliott] There’s not really a technique.
    I’ve been measuring speeds all my life.

    Q. And the radar serves what function in relation to
    your visual observation of the speed of the vehicle?

    A. It’s just a second opinion that already corrobo-
    rates what you already know.

J.A. 24.

    Q. [Defense counsel] You testified earlier that there
    was no technique to estimating speed. You use no
    technique; is that correct?

    A. [Deputy Elliott] You don’t need a technique. It’s
    all based on your training and experience. As long as
    you have a tracking history and you have experience
    in observing speeds.

    Q. So you can just basically look at a vehicle and
    guess.

    A. There’s no guessing about it. It’s an estimation
    based on tracking history and my training and expe-
    rience.

    Q. Based on tracking history.

    A. That’s correct.

    Q. Which would be?
                  UNITED STATES v. SOWARDS                  5
    A. Being able to sufficiently see that vehicle, that
    vehicle coming towards me, that vehicle passing me,
    me being able to estimate that vehicle’s speed.

    Q. And generally how long [did] you watch [Sow-
    ards’s] vehicle?

    A. At this point in time [Sowards] was approxi-
    mately a hundred yards out before he was in front of
    me.

    Q. Football field.

    A. Approximately.

    Q. Approximately. So you can estimate distance.

J.A. 80-81.

  Subsequently, however, Deputy Elliott testified that he did
not measure the distance that he tracked Sowards’s vehicle
and that his testimony of 100 yards of tracking history was an
approximation rather than a certainty. Furthermore, on cross-
examination, and when questioned directly by the district
court about his knowledge of distances, Deputy Elliott gave
several inconsistent and incorrect answers regarding measure-
ments:

    Q. [Government counsel] And how many feet are in
    a hundred yards?

    A. [Deputy Elliott] There’s 12 feet in a yard.

    Q. So 300 feet?

    A. Correct.

J.A. 109.
6                 UNITED STATES v. SOWARDS
    THE COURT: And how many feet are in a yard?

    [Deputy Elliott]: How many feet? There’s 12 feet in
    a yard.

    THE COURT: Well, do you know what a yardstick
    is?

    [Deputy Elliott]: Yes, sir.

    THE COURT: How many inches in a yardstick?

    [Deputy Elliott]: Well, on a yardstick there’s 12
    inches. Well, it depends on the yard stick that . . .
    you have.

    THE COURT: Use your hands to indicate a yard-
    stick.

    [Deputy Elliott]: A yardstick is about that long (indi-
    cating).

    THE COURT: All right. And how many inches are
    in it?

    THE WITNESS: Four foot in a yard.

J.A. 116.

   Thereafter, Deputy Elliott testified that his visual estima-
tion of the speed of Sowards’s vehicle was not dependent on
his ability to estimate the distance that it traveled.

    Q. [Defense counsel] So how can you estimate speed
    without knowing the distance?

    A. [Deputy Elliott] Because of my visual observa-
    tion. I know that it takes a quicker time for vehicles
                  UNITED STATES v. SOWARDS                     7
    to come at me at 75 miles per hour versus the 70
    miles per hour zone in that area. The reason why I
    know that is because I’ve been working that area for
    approximately four and a half years. I’ve conducted
    radar enforcement. I’ve also conducted speed esti-
    mations upon my estimation of vehicles that I see
    that I work that area on a daily basis.

J.A. 80.

    Q. Well, how can you be certain that [Sowards’s
    vehicle] was going 75 miles an hour?

    A. My training and experience.

    ...

    Q. Could you explain the specifics of your visual
    estimation training as far as how you arrive at a
    speed.

    A. Because I know a vehicle traveling 75 miles per
    hour, it gets faster to me than a vehicle that’s travel-
    ing 70 miles per hour by my visual observation.

J.A. 93-94.

   The district court denied Sowards’s motion to suppress,
rejecting Sowards’s arguments and finding that Deputy Elliott
had probable cause to initiate the traffic stop of Sowards’s
vehicle:

    Officer Elliott had probable cause to believe a traffic
    violation had occurred based on speed. He’s trained
    to estimate speeds. His difficulty with measurements
    is immaterial to his estimate of speed as that did not
    depend on time or distance. And the certification that
    he received, I believe three times, depended on accu-
8                     UNITED STATES v. SOWARDS
        racy in estimating speeds. So he had a particularized
        and objective basis for suspecting that a traffic viola-
        tion had occurred.

J.A. 121. Subsequently, Sowards entered a conditional guilty
plea, reserving the right to appeal any issues related to his
suppression motion. At the sentencing hearing, the district
court sentenced Sowards to 70 months’ imprisonment, which
was the low end of the Sentencing Guidelines range.2 Sowards
filed a timely notice of appeal.

                                   II.

                                   A.

   The issue on appeal is whether Deputy Elliott’s traffic stop
of Sowards’s vehicle was supported by probable cause and,
accordingly, whether the district court properly denied Sow-
ards’s motion to suppress the evidence seized from the car as
a result of the traffic stop.

   We review the district court’s legal determinations de novo
and its factual determinations for clear error. United States v.
Moreland, 437 F.3d 424, 429 (4th Cir. 2006). Under the clear
error standard, "[a] factual finding by the district court may be
reversed only if, ‘although there is evidence to support it, the
reviewing court on the entire evidence is left with the definite
and firm conviction that a mistake has been committed.’"
Walton v. Johnson, 440 F.3d 160, 173-74 (4th Cir. 2006) (en
banc) (quoting United States v. U.S. Gypsum Co., 333 U.S.
364, 395 (1948)). The evidence is construed in the light most
favorable to the Government, the prevailing party below.
United States v. Seidman, 156 F.3d 542, 547 (4th Cir. 1998).

    Our review of the district court’s docket reveals that Sowards served
    2

his entire prison sentence and began a three year period of supervised
release on May 20, 2011.
                      UNITED STATES v. SOWARDS                            9
    The Fourth Amendment guarantees "[t]he right of the peo-
ple to be secure in their persons, houses, papers, and effects,
against unreasonable searches and seizures." U.S. Const.
amend. IV. "When a police officer stops an automobile and
detains the occupants briefly, the stop amounts to a seizure
within the meaning of the Fourth Amendment." United States
v. Digiovanni, 650 F.3d 498, 506 (4th Cir. 2011) (citing
Whren v. United States, 517 U.S. 806, 809-10 (1996)). "[T]he
underlying command of the Fourth Amendment is always that
searches and seizures be reasonable." Wilson v. Arkansas, 514
U.S. 927, 931 (1995); see also Whren, 517 U.S. at 810 ("An
automobile stop is thus subject to the constitutional impera-
tive that it not be ‘unreasonable’ under the circumstances.").
"As a general matter, the decision to stop an automobile is
reasonable where the police have probable cause to believe
that a traffic violation has occurred." Id. Probable cause exists
if, given the totality of the circumstances, the officer "had rea-
sonably trustworthy information . . . sufficient to warrant a
prudent [person] in believing that the petitioner had commit-
ted or was committing an offense." Beck v. Ohio, 379 U.S. 89,
91 (1964); see also Porterfield v. Lott, 156 F.3d 563, 569 (4th
Cir. 1998).

   Accordingly, our inquiry here is whether, given the totality
of the circumstances, Deputy Elliott had reasonably trustwor-
thy information sufficient to support a prudent person’s belief
that Sowards was speeding.3
   3
     To appreciate the difference in view expressed by our colleague in dis-
sent, it is worthy to note that the dissenting opinion urges this Court to
undertake a probable cause inquiry by reference to what probable cause
is not. See post at 32 ("The probable-cause standard does not even require
that the officer’s belief be more likely true than false." (quotation marks
omitted)). We, however, decline to adopt this analytical approach; proba-
ble cause is the threshold that protects citizens from unreasonable searches
and seizures that violate the Fourth Amendment to the Constitution and,
therefore, our focus is on what probable cause does require. For probable
cause to mean anything, it has to mean something. See Brinegar v. United
States, 338 U.S. 160, 175-76 (1949) ("The substance of all the definitions
10                    UNITED STATES v. SOWARDS
                                    B.

   The district court found that "Officer Elliott had probable
cause to believe a traffic violation had occurred" because
Officer Elliott was "trained to estimate speeds" and because
"the certification that he received . . . depended on accuracy
in estimating speeds." J.A. 121. The district court also found
that Officer Elliott’s "difficulty with measurements is immate-
rial to his estimate of speed as that did not depend on time or
distance." Id. Based on these findings, the district court con-
cluded that Officer Elliott "had a particularized and objective
basis for suspecting that a traffic violation had occurred." Id.

   We hold, based on the record before us, that several of the
district court’s material factual findings were clearly errone-
ous.

   First, it was clear error for the district court to find that
Deputy Elliott was "trained to estimate speeds." J.A. 121.
Contrary to this finding, the record indicates that Deputy
Elliott was trained to use a radar unit. Rather than being
"trained to estimate speeds," Deputy Elliott was given the
opportunity to "guess" the speed of twelve vehicles and, in
doing so, he demonstrated the proficiency of guessing within
a total margin of error of 42 mph for all twelve of those vehi-
cles. There was no testimony or evidence that Deputy Elliott
received any specialized training in the estimation of vehicle
speeds. In fact, Deputy Elliott’s testimony confirmed that he
used absolutely no technique or method to visually guess
vehicle speeds. Given this testimony, and the absence of con-

of probable cause is a reasonable ground for belief of guilt. . . . To allow
less would be to leave law-abiding citizens at the mercy of the officers’
whim or caprice."); Wong Sun v. United States, 371 U.S. 471, 479 (1963)
("The history of the use, and not infrequent abuse, of the power to arrest
cautions that a relaxation of the fundamental requirements of probable
cause would leave law-abiding citizens at the mercy of the officers’ whim
or caprice." (quotation marks omitted)).
                       UNITED STATES v. SOWARDS                             11
trary evidence in the record, it was clearly erroneous for the
district court to find that Deputy Elliott was trained to esti-
mate speeds.4 Cf. State v. Estes, 223 P.3d 287, 290-91 (Idaho
Ct. App. 2009) (holding that certified officer’s visual speed
estimate was insufficient to convict defendant of speeding,
where officer’s testimony failed to reveal precise accuracy
rates and margin of error for his visual speed estimates during
certification).5

   Second, it was clear error for the district court to find that
Deputy Elliott’s "difficulty with measurements is immaterial
to his estimate of speed as that did not depend on time or dis-
  4
     Our colleague in dissent disputes this conclusion by noting Deputy
Elliott’s "uncontradicted testimony" that "a certified instructor . . .
‘showed him how to estimate the speeds’ of vehicles." Post at 49 ("That
sounds like training to me."). The record does not support the dissent’s
view. First, the "certified instructor" Deputy Elliott identified was a "certi-
fied radar operator" who "show[ed Deputy Elliott] how to work the
radar." J.A. 23 (emphasis added). There is no evidence that this instructor
was certified or otherwise qualified to "train" Deputy Elliott in how to
visually estimate the speeds of vehicles. Second, immediately after giving
this "uncontradicted testimony," post at 49, Deputy Elliott directly contra-
dicted it. See J.A. 24 ("Q: And do you learn certain techniques in visually
determining the speed of the vehicle?" A: "There’s not really a tech-
nique.").
   5
     The district court’s decision to qualify Deputy Elliott as an expert in
the unaided visual estimation of vehicle speed was clearly inconsistent
with the requirement of Rule 702 of the Federal Rules of Evidence "that
[expert] testimony . . . be the product of reliable principles and methods."
United States v. Baptiste, 596 F.3d 214, 222 (4th Cir. 2010); see also
United States v. Johnson, 617 F.3d 286, 294 (4th Cir. 2010) (stating that
experts "must use reliable principles and methods, and apply those princi-
ples and methods reliably to the facts of the case."). Although the court’s
role as "gatekeeper," in ensuring that expert testimony is "reliable and rel-
evant," Kumho Tire Co. v. Carmichael, 526 U.S. 137, 149 (1999), is cons-
tant throughout all judicial proceedings, we recognize that the "Federal
Rules of Evidence[, apart from testimonial privileges,] do not apply at
suppression hearings." United States v. Schaefer, 87 F.3d 562, 570 (1st
Cir. 1996); Fed. R. Evid. 104(a). As such, we need not and do not address
the district court’s inexplicable determination to qualify Deputy Elliott as
an expert.
12                    UNITED STATES v. SOWARDS
tance." J.A. 121. This finding rings in the absurd because one
cannot discern a speed of a vehicle measured in miles-per-
hour without discerning both the increment of distance trav-
eled and the increment of time passed. Indeed, the very defini-
tion of speed derives from the mathematical formula of
distance divided by time. See, e.g., Warboys v. Proulx, 303 F.
Supp. 2d 111, 116 n.6 (D. Conn. 2004) ("To calculate average
speed, one divides the distance traveled by the time it took to
travel this distance. [distance ÷ time = speed . . .]"). This
Court may properly take judicial notice of this formula. See,
e.g., Ballantine v. Cent. R.R. of New Jersey, 460 F.2d 540,
543 (3rd Cir. 1972).6

   Furthermore, the materiality of Deputy Elliott’s "difficulty
with measurements" was established by Deputy Elliott’s own
testimony. During the suppression hearing, Deputy Elliott
exhibited a notable absence of fluency in his knowledge of
distance measurements. Deputy Elliott testified that: (1)
"There’s 12 feet in a yard," J.A. 109, 116; (2) "300 yards
would be a [100] yards," J.A. 109; and (3) "on a yardstick
there’s 12 inches." J.A. 116. Deputy Elliott also testified that
the number of inches on a yard stick "depends on the yard
stick," J.A. 116, and that math could change "depend[ing] on
the person who’s behind it." J.A. 88. In light of this testi-
mony, it is material—and indeed troubling—that Deputy
   6
     Our dissenting colleague contends that "there is no evidence [in the
record] that the reliability of an officer’s visual estimation of speed is or
should be tied to a specific or minimum distance or time." Post at 49. If
the dissent believes estimation of speed is not tied to distance or time,
what then would be the dissent’s mathematical formula for speed? With-
out a consideration of a specific distance and time, we are left with Deputy
Elliott’s purely speculative guess of the speed of Sowards’s vehicle.
That’s not enough to establish probable cause. See, e.g., Terry v. Ohio,
392 U.S. 1, 21-22 (1968) (predicating reasonable suspicion—a less robust
standard than probable cause—on the existence of "specific and articul-
able facts" and "rational inferences from those facts" because "[a]nything
less would invite intrusions upon constitutionally guaranteed rights based
on nothing more substantial than inarticulate hunches, a result this Court
has consistently refused to sanction." (emphasis added)).
                       UNITED STATES v. SOWARDS                             13
Elliott asserted that his visual estimates of speed are depen-
dent on his observation of the "tracking history" of a vehicle.
See, e.g., J.A. 81 (testifying that: (1) a technique is not
required to estimate speeds "[a]s long as you have a tracking
history . . . ."; and (2) his method of estimating speed is not
a guess because "[i]t’s an estimation based on tracking history
. . . ."). Given that Deputy Elliott further testified that he had
"a hundred yards" of tracking history on Sowards’s vehicle to
estimate its speed, J.A. 81, it was clearly erroneous for the
district court to find that Deputy Elliott’s difficulty with mea-
surements was immaterial to his estimate of the speed of Sow-
ards’s vehicle.7

                                      C.

  Notwithstanding these two clearly erroneous factual find-
ings by the district court, the Government contends that Dep-
uty Elliott’s visual speed estimate, standing alone, provided
probable cause for Deputy Elliott to initiate a traffic stop of
Sowards’s vehicle for speeding.8
  7
     The dissent points to the absence of "evidence [in the record] that
North Carolina’s certification procedure for estimating speeds is depen-
dent upon distance or time." Post at 49-50. This assertion is misleading
and misplaced; the former because, rather than a "certification" for "esti-
mating speeds," Deputy Elliott’s certification was for the use of radar; the
latter because, if not distance and time, then on what basis would a hypo-
thetical certification in visual speed estimation in miles (distance) per hour
(time) depend?
   8
     The Government relies on an unpublished opinion of this Court—
decided without oral argument and issued per curiam. See United States
v. Daras, No. 98-4286, 1998 WL 726748, at *2 (4th Cir. Oct. 16, 1998)
(per curiam) ("[T]he Government correctly points out that the officer’s
visual estimate is also sufficient, by itself, to support a conviction."). This
case is not binding. The Government also relies on a non-binding and
materially distinguishable decision issued by a district court in United
States v. Wornom, 754 F. Supp. 517, 519 (W.D.Va. 1991) (where radar
evidence was suppressed, affirming conviction of defendant for speeding
based on officer’s visual speed estimate).
14                    UNITED STATES v. SOWARDS
   However, the Fourth Amendment does not allow, and the
case law does not support, blanket approval for the proposi-
tion that an officer’s visual speed estimate, in and of itself,
will always suffice as a basis for probable cause to initiate a
traffic stop. Instead, for the purposes of the Fourth Amend-
ment, the question remains one of reasonableness. Critically,
and as further explained below, the reasonableness of an offi-
cer’s visual speed estimate depends, in the first instance, on
whether a vehicle’s speed is estimated to be in significant
excess or slight excess of the legal speed limit. If slight, then
additional indicia of reliability are necessary to support the
reasonableness of the officer’s visual estimate.9

   The standard for evidence to convict is more exacting than the standard
sufficient to support probable cause. See Porterfield, 156 F.3d at 569.
However, a speeding violation presents a unique circumstance, see United
States v. Moore, No. 10 Cr. 971 (RJH), slip op. at *5 (S.D.N.Y. Dec. 19,
2011), because reliable evidence of the vehicle’s speed generally provides
the objectively reasonable basis for probable cause to initiate the traffic
stop. Although our discussion of the permissible uses of visual speed esti-
mates relies on probable cause cases, we also include references to a lim-
ited number of conviction cases where comparisons are useful.
   9
     Our colleague in dissent expresses the policy view that this reasonable-
ness requirement "ignores the realities of traffic enforcement and unduly
ties the hands of officers" because "as a practical matter" the requirement
is "unworkable for police officers." Post at 36-37, 50. Such policy consid-
erations are best left to the legislative branch of government, which is bet-
ter suited to decide them.
   When a state legislature does decide to take up this issue, it may want
to take note of some of the troubling implications of the dissent’s view.
For instance, allowing police officers to rely, without support, exclusively
on their subjective impressions that a vehicle is traveling in slight excess
of the legal speed limit may disincentivize the use of verifiable methods
and technology. Indeed, in this case, Deputy Elliot’s vehicle was equipped
with radar and he intentionally positioned himself such that it could not
be used.
   Furthermore, because an officer’s subjective intentions for initiating a
traffic stop are not relevant, see Whren, 517 U.S. at 813 ("Subjective
intentions play no role in ordinary, probable-cause Fourth Amendment
                      UNITED STATES v. SOWARDS                          15
                                    1.

   In United States v. Ludwig, our sister Circuit framed this
analysis similarly in holding that "an officer’s visual estima-
tion can supply probable cause to support a traffic stop for
speeding in appropriate circumstances." 641 F.3d 1243, 1247
(10th Cir.) (emphasis added), cert. denied, 132 S. Ct. 306
(2011). Although Ludwig did not elaborate on the circum-
stances that may make a visual speed estimate appropriate to
supply probable cause, we find that at a minimum there must
be sufficient indicia of reliability for a court to credit as rea-
sonable an officer’s visual estimate of speed.

   Thus, where an officer estimates that a vehicle is traveling
in significant excess of the legal speed limit, the speed
differential—i.e., the percentage difference between the esti-
mated speed and the legal speed limit—may itself provide
sufficient "indicia of reliability" to support an officer’s proba-
ble cause determination. See, e.g., United States v. Banks, No.
2:08-cr-19-FtM-29SPC, 2008 WL 4194847, at *1, *4
(M.D.Fla. Sep. 11, 2008) (finding probable cause where offi-
cer observed vehicle "traveling at a high rate of speed," esti-
mated to be 50-60 mph in a 30-mph zone, making it
"extremely obvious to [the officer] that the vehicle was speed-
ing"); State v. Butts, 269 P.3d 862, 873 (Kan. Ct. App. 2012)

analysis."), erosion of the Fourth Amendment’s objective reasonableness
requirement effectively eliminates any protection against profiling and
arbitrary detentions. Cf. Chicago v. Morales, 527 U.S. 41, 71 (1999)
(Breyer, J., concurring) ("The ordinance is unconstitutional, not because
a policeman applied []his discretion wisely or poorly in a particular case,
but rather because the policeman enjoys too much discretion in every
case") (emphasis in original); United States v. Sokolow, 490 U.S. 1, 12
(1989) (Marshall, J., dissenting) ("[T]he Fourth Amendment protects inno-
cent persons from being subjected to "overbearing or harassing" police
conduct carried out solely on the basis of imprecise stereotypes of what
criminals look like, or on the basis of irrelevant personal characteristics
such as race.") (quoting Terry v. Ohio, 392 U.S. 1, 14-15, and n.11
(1968)).
16                 UNITED STATES v. SOWARDS
(finding reasonable suspicion where officer "estimated vehi-
cle speed [was 45 mph in a 30-mph zone, which was] signifi-
cantly higher than the posted speed limit and, as a result, a
difference that would be discernable to an observant and
trained law enforcement officer"); cf. People v. Olsen, 239
N.E.2d 354, 355 (N.Y. 1968) (holding officer’s visual speed
estimate of vehicle traveling 50-55 mph in a 30-mph zone suf-
ficient to support speeding conviction).

   However, where an officer estimates that a vehicle is trav-
eling in only slight excess of the legal speed limit, and partic-
ularly where the alleged violation is at a speed differential
difficult for the naked eye to discern, an officer’s visual speed
estimate requires additional indicia of reliability to support
probable cause. See United States v. Moore, No. 10 Cr. 971
(RJH), slip op. at *6 (S.D.N.Y. Dec. 19, 2011) (finding that
stop was unsupported by probable cause and explaining that,
absent an officer’s estimate that a vehicle is traveling "signifi-
cantly in excess" of the legal speed limit, "courts will credit
an officer’s testimony regarding firsthand observation of a
speeding vehicle if additional, specific details of his or her
account confirm that the officer’s observation and belief were
reasonable"); cf. City of Kansas City v. Oxley, 579 S.W.2d
113, 116 (Mo. 1979) (holding that officer’s uncorroborated
opinion evidence of defendant’s 45-mph speed in a 35-mph
zone was insufficient evidence to allow trier of fact to find
that defendant was speeding); Olsen, 239 N.E.2d at 355
("[A]bsent mechanical corroboration, [testimony] that a vehi-
cle was proceeding at 35 or 40 miles per hour in [a 30-mph]
zone might for obvious reason be insufficient [to sustain a
conviction for speeding], since it must be assumed that only
a mechanical device could detect such a slight variance with
[sufficient] accuracy."); State v. Kimes, 234 S.W.3d 584, 589
(Mo. Ct. App. 2007) ("[W]here an officer’s estimation of
speed is 60 m.p.h., a fact-finder cannot conclude with any
degree of certainty that a defendant was exceeding a 55 m.p.h.
speed limit because the accuracy of human estimation of
speed cannot easily, readily, and accurately discriminate
                  UNITED STATES v. SOWARDS                  17
between such small variations in speed."); Peoples Drug
Stores v. Windham, 12 A.2d 532, 537 (Md. 1940) ("[A]n esti-
mate is necessarily approximate and not exact for without
mechanical aides it is manifestly impossible for any one . . .
to estimate precisely the speed of a moving object, and that
fact is assumed by every one possessing ordinary common
sense.").

   The reasonableness of an officer’s visual estimate that a
vehicle is traveling in slight excess of the legal speed limit
may be supported by radar, pacing methods, or other indicia
of reliability that establish, in the totality of the circum-
stances, the reasonableness of the officer’s visual speed esti-
mate. See e.g., United States v. Gomez Valdez, No.
4:10CR3100, 2011 WL 5037190, at *4 (D.Neb. Sept. 12,
2011) (finding probable cause where officer’s visual estimate
was verified by radar confirming that defendant was traveling
70-mph in a 65-mph zone); United States v. Nunez, No. 1:10-
CR-127, 2011 WL 2357832, at *1 (D.Utah June 9, 2011)
(finding reasonable suspicion where officer’s visual estimate
was supported by pacing, which confirmed that defendant was
traveling 85 mph in a 75-mph zone); United States v. Colden,
No. 11-M-989-SKG, 2011 WL 5039777, at *1, *2 (D.Md.
Oct. 21, 2011) (holding that officer’s "visual estimation of
defendant’s speed, in combination with the officer’s observa-
tions that his car shook [when defendant’s car passed] and
that defendant tapped his brakes, amounts to a reasonable
articulable suspicion that defendant was speeding"); United
States v. Fuentes, No. 09 Cr. 860, 2010 WL 707424, at *3
(S.D.Tex. Feb. 23, 2010) (finding reasonable suspicion where
officer’s visual speed was supported by additional
observations—i.e., vehicle’s relative speed and roaring engine
—and such observations were corroborated by patrol car’s
video camera); United States v. Riley, No. 07 Cr. 226, 2007
WL 3204063, at *4 (D.Neb. Oct. 30, 2007) (finding reason-
able suspicion where officer’s visual speed estimate was sup-
ported by separate radio dispatch indicating defendant’s
vehicle was driving recklessly).
18                     UNITED STATES v. SOWARDS
   Such additional indicia of reliability need not require great
exactions of time and mathematical skill that an officer may
not have, but they do require some factual circumstance that
supports a reasonable belief that a traffic violation has
occurred. In the absence of sufficient additional indicia of
reliability, an officer’s visual approximation that a vehicle is
traveling in slight excess of the legal speed limit is a guess
that is merely conclusory and which lacks the necessary fac-
tual foundation to provide an officer with reasonably trust-
worthy information to initiate a traffic stop.10 See Moore,
2011 WL 6325973, at *8; State v. Petzoldt, No. 10-0861,
2011 WL 2556961, at *3–4 (Iowa Ct. App. June 29, 2011)
(holding that "[w]ithout the facts upon which [the police offi-
cer] formed his belief that [defendant’s] truck was speeding,
we cannot determine whether his belief was reasonable", not-
withstanding officer’s testimony that "he believed [defendant]
was traveling at a speed greater than the posted speed limit"
and officer’s 31 years of experience).

                                      2.

   Here, Deputy Elliott opined, based on his visual observa-
tion alone, that Sowards’s vehicle was traveling 75 mph in a
70-mph zone. Deputy Elliott did not corroborate his opinion
with radar, pacing, or otherwise. Furthermore, Deputy
Elliott’s opinion was not supported by sufficient additional
  10
     Our colleague in dissent contends that any requirement for corrobora-
tion of an officer’s unaided visual approximation of a slight speeding vio-
lation is an unprecedented gloss on the traditional totality of the
circumstances test. This Court, however, has held that where the basis for
probable cause is inherently unreliable, then this basis must be corrobo-
rated such that it exhibits sufficient indicia of reliability. See, e.g., United
States v. Massenburg, 654 F.3d 480, 486 (4th Cir. 2011) ("Reliance on an
anonymous tip may be reasonable [for Terry frisk] where, suitably corrob-
orated, it exhibits sufficient indicia of reliability." (quotation marks omit-
ted)); United States v. Reaves, 512 F.3d 123, 126 (4th Cir. 2008) ("When
the police rely on an anonymous tip to support reasonable suspicion, the
tip must be accompanied by some corroborative elements that establish its
reliability." (quotation marks omitted)).
                       UNITED STATES v. SOWARDS                            19
indicia of reliability. Therefore, standing alone, Deputy
Elliott’s visual speed estimate—made at a speed differential
of only 5 mph at a high rate of speed11—did not provide Dep-
uty Elliott with "reasonably trustworthy information . . . suffi-
cient to warrant a prudent [person] in believing that [Sowards]
had committed" a speeding violation. Beck, 379 U.S. at 91.

  We agree that "the accuracy of human estimation of speed
cannot easily, readily, and accurately discriminate between
such small variations in speed."12 Kimes, 234 S.W.3d at 589;
  11
     To illustrate the slight differential in the time to travel a distance of
100 yards at a speed of 75 mph versus 70 mph, we need only calculate the
yards per second for each speed. At 70 mph, a vehicle travels 34.22 yards
per second and, thus, 100 yards in 2.92 seconds, whereas at 75 mph a
vehicle travels 36.67 yards per second and, thus, 100 yards in 2.73 sec-
onds. [yards per second = (miles per hour x 1760) ÷ 3600, where 1760
is the number of yards in a mile, and where 3600 is the number of seconds
in an hour. Therefore: (a) 34.22 yd/sec = (70 mph x 1760) ÷ 3600 and,
thus, 2.92 seconds = 100 yards ÷ 34.22 yd/sec; and (b) 36.67 yd/sec = (75
mph x 1760) ÷ 3600; and, thus, 2.73 seconds = 100 yards ÷ 36.67 yd/sec]
   To accept the conclusion that Deputy Elliott can visually discern that a
vehicle is traveling at 75 mph in a 70-mph zone is to accept the conclusion
that he can visually discern a differential in time of less than one-fifth of
one second for a vehicle traveling 75 mph versus 70 mph over a distance
that he could only approximate to be about 100 yards. Of course, this is
also assuming—which the evidence does not support—that the distance
traveled by Sowards’s vehicle was indeed 100 yards, and, moreover, this
is without consideration of Deputy Elliott’s notable and material difficul-
ties with measurements in yards.
   12
      Our colleague in dissent contends this conclusion is unsupported by
"expert testimony, or other evidence." Post at 38. However, in United
States v. Foster, 662 F.3d 291, 295 (4th Cir. 2011), petition for cert. filed,
___ U.S.L.W. ___ (U.S. June 4, 2012) (No. 11-10744), this Court
approved the use of "common sense" in "draw[ing] reasonable inferences"
from the record because, as Senior Judge Hamilton explained, "[t]he use
of common sense is not the equivalent of fact-finding." 662 F.3d at 298
(Hamilton, J., concurring). Indeed, "[e]ven appellate judges are endowed
with brains in the hope and expectation that they will be used to obvious
purpose. . . . There are worse fates for a judicial decision than to have it
align with the practical virtues of logic and common sense." United States
20                    UNITED STATES v. SOWARDS
see also Olsen, 239 N.E.2d at 355. Unlike Ludwig, where the
court noted that there was "no affirmative reason to think that
the trooper[’s] . . . estimate should be discredited," 641 F.3d
at 1247, here the record reflects myriad reasons to discredit,
and no reason to credit, Deputy Elliott’s estimate.

   Therefore, we conclude that Deputy Elliott’s visual speed
estimate was in fact a guess that was merely conclusory, with-
out an appropriate factual foundation, and simply lacking in
the necessary indicia of reliability to be an objectively reason-
able basis for probable cause to initiate a traffic stop.

                                    III.

   We address separately our dissenting colleague’s primary
contention that the record supports a finding of Deputy
Elliott’s expertise in the visual estimation of vehicle speeds
within an average 3.5-mph margin of error. Post at 26, 28,
33-34, 38, 47, 51-52. On the basis of this contention, the dis-
sent "believe[s] the government has easily established that
Deputy Elliott . . . had probable cause to stop Sowards’s vehi-
cle" for traveling 75 mph in a 70-mph zone. Post at 35. Thus,
in the view of the dissent, Sowards’s constitutional right to be
free from unreasonable seizures is overcome by Deputy
Elliott’s purported "expertise," which in turn depends on the
"road test" Deputy Elliott satisfied as part of his radar certifi-
cation.

v. Foster, 674 F.3d 391 (4th Cir. 2012) (Wilkinson, J., concurring in the
denial of rehearing en banc).
   This is particularly appropriate in this context because probable cause
"is not defined by bright lines and rigid boundaries" but "allows a [judicial
officer] to review the facts and circumstances as a whole and make a com-
mon sense determination" whether an objectively reasonable basis exists
for the challenged search or seizure. United States v. Henry, 673 F.3d 285,
290 (4th Cir. 2012) (quotation marks omitted), petition for cert. filed, ___
U.S.L.W. ___ (U.S. May 30, 2012) (No.11-10610).
                   UNITED STATES v. SOWARDS                  21
   We accord Deputy Elliott no such expertise, as there is no
indication in the record that this road test was designed or
intended as an evaluation of Deputy Elliott’s ability to esti-
mate vehicle speeds in any context other than in conjunction
with radar. Indeed, one thing we know about the road test is
that Deputy Elliott was required to estimate the speeds of "12
separate vehicles . . . and then corroborate [his] visual calcu-
lations with the use of a radar[.]" J.A. 24-25 (emphasis
added) (A: "[T]hat’s when the certified [radar] instructor
takes off the piece of paper off your radar unit and advises
you what the actual clock was."). Thus, to the extent that the
road test prepared Deputy Elliott to visually estimate vehicle
speeds, it did so only to the extent subsequently corroborated
by radar, which, in this case, Deputy Elliott failed to do.

   The record also reflects that Deputy Elliott may have
passed the road test but nonetheless "be[en] off up to 12 miles
an hour on [any] one vehicle" and "42 miles per hour" on all
twelve vehicles. J.A. 26. Consequently, it is entirely possible
that Deputy Elliott’s visual estimates were off by six mph on
seven vehicles and perfect on the other five vehicles. In such
case, although Deputy Elliott’s "average" or "mean" margin
of error would have been only 3.5-mph per vehicle, his "me-
dian" and "mode" margin of error would have been six mph
per vehicle. Given that we are faced here with a mere five
mph differential, those hypothetical results—as equally possi-
ble as those presented by the dissent—would seem to call into
question the dissent’s probable cause analysis concerning the
inherent reliability of Deputy Elliott’s unaided visual estimate
of speed.

   The record further shows that Deputy Elliott made his
visual speed estimates, not "in a test environment . . . where
the situation is controlled," but instead "on the street with
actual drivers." J.A. 25. Presumably—although, again, this is
unknown—the vehicle speeds of these "actual drivers" were
impacted by the speed limit in the area tested, as well as the
presence of police officers conducting a radar test. In any
22                    UNITED STATES v. SOWARDS
case, to the extent one would allow Deputy Elliott to use the
results of this road test to overcome Sowards’s constitutional
right to be free from unreasonable seizures, prudency dictates
the consideration of these and other questions relevant to the
road test’s design and reliability. Cf. People v. Palermo, 2009
WL 8474301 (N.Y. City Ct. Sept. 28, 2009) (notwithstanding
officer’s testimony "that he passed an examination," finding
that traffic stop lacked probable cause because officer failed
to testify about type of training, length of training, or content
of training); Estes, 223 P.3d at 290-91 (same).

   The dissent overlooks these and other shortcomings, and
would instead find probable cause on the basis of Deputy
Elliott’s "demonstrated an[d] uncontradicted ability to visu-
ally estimate the speed of vehicles within an average margin
of error of 3.5 mph per vehicle." Post at 33-34. Indeed, under
this line of reasoning, our colleague in dissent would appar-
ently permit traffic stops on the basis of an officer’s uncorrob-
orated and unsupported visual estimate that a vehicle is
traveling 71 mph in a 70-mph zone.13 See post at 39 (citing
with approval State v. Singh, No. F-98-022, 1999 WL 355270,
at *1 (Ohio Ct. App. 1999), where court noted officer’s testi-
mony that his visual estimates were accurate within 1-2 mph).14
Following the dissent’s approach to its logical conclusion, we
see no limits upon an officer’s, such as Deputy Elliott’s, pow-
ers of speed estimation. Nevertheless, it defies all reason to
believe that Deputy Elliott, particularly in light of his diffi-
culty with distances, would be able to accurately estimate
with his vision alone, within the same 3.5-mph margin of
   13
      It is worth noting that the dissent has not cited—nor have we found—
a single case issued by any court at any time, whether state or federal,
finding probable cause exists to initiate a traffic stop for speeding on the
sole basis of an officer’s unaided visual estimate that a vehicle was
exceeding the speed limit by five mph or less.
   14
      As discussed, this and other cases in Ohio standing for the proposition
that officers may use unaided visual estimates of speed for arrest, charg-
ing, and conviction have been superseded and overruled by legislation. See
Ohio Rev. Code § 4511.091(C)(1).
                   UNITED STATES v. SOWARDS                  23
error, the speed of a car traveling ten mph, 25 mph, 50 mph,
75 mph, 100 mph, 150 mph, or, presumably, a plane traveling
700 mph.

   A short example from our national pastime seems particu-
larly apt here. One year ago, the fastest pitch in the annals of
baseball history was recorded: 106 mph, by Cincinnati Reds
left-handed pitcher Aroldis Chapman. See Jeff Passan, Chap-
man’s 106-mph fastball was likely bogus, YAHOO SPORTS,
April 19, 2011, HTTP://sports.yahoo.com/mlb/news?
slug=jp-passan_aroldis_chapman_106_radar_reds_fastball_
controversy_041911 (last visited April 26, 2012). While the
pitch itself is remarkable in its own right, a sports reporter
noted a perhaps even more interesting phenomenon associated
with the actual measurement of that pitch as "three nuggets of
information started to parade themselves as facts." Id. Specifi-
cally, the radar connected to the scoreboard showed the speed
as 106 mph, the television broadcast’s radar reflected that it
was 105 mph, while the radar system used by Major League
Baseball, which utilizes three cameras on a single pitch that
calculate each pitch’s speed more than 50 times, pegged the
pitch at only 102.4 mph. Id. In light of three seemingly unim-
peachable, entirely reliable sources, the writer was left with
the inevitable question, "How can one pitch travel three dif-
ferent velocities?" Id. The writer went on to surmise that
"[u]nless one of Chapman’s fastballs voyaged through the
Matrix, another in the Source Code and the third in reality, it
leaves us with a question more appropriate for a philosophy
class than a baseball discussion." Id.

   Indeed, in the world of baseball, there are even more abso-
lutes than the facts presented in this case. For example, the
distance between the pitcher’s mound and home plate is fixed
at 60 feet 6 inches; likewise, the clip of Chapman’s fastball
has now been viewed more than 500,000 times online. See,
e.g., http://www.youtube.com/watch?v= HbBh0NsNisQ (last
visited April 26, 2012). Even so, and presumably despite
24                    UNITED STATES v. SOWARDS
efforts by so-called experts like Deputy Elliott in visual speed
estimation, the controversy remains.

   Here, the dissent’s contention that Deputy Elliott’s estimate
may be unreliable, uncorroborated and unsupported and yet
still comport with the "reasonableness" threshold of the
Fourth Amendment, is not—and cannot be—the law. We hold
that the objective unreliability of Deputy Elliott’s uncorrobo-
rated and unsupported visual estimate is categorically irrecon-
cilable with Beck’s requirement for "reasonably trustworthy
information" to serve as the foundation for probable cause.
379 U.S. at 91. Deputy Elliott’s visual estimate that Sow-
ards’s vehicle was traveling 75 mph was the sole basis of his
probable cause to initiate the traffic stop and subsequent sei-
zure of Sowards’s vehicle. As such, the seizure was constitu-
tionally unreasonable, and the evidence gathered pursuant to
the search must be suppressed.

   Notwithstanding the dissent’s protestations, the sky will not
fall as a result of today’s majority decision.15 According to the
dissent it is "[i]ronic[ that] while a lay person can estimate the
speed of [ ] a vehicle based upon his or her personal observa-
tions, an experienced and trained police officer no longer
  15
    Indeed, in the wake of Ohio Supreme Court’s decision in City of Bar-
berton v. Jenney, 929 N.E.2d 1047 (Ohio 2010), cert. denied, 131 S. Ct.
517 (2010), which would have allowed a police officer’s unaided visual
estimation to suffice for the purposes of a speeding conviction, the Ohio
legislature moved swiftly to amend its existing laws to provide, subject to
limited exception: "No person shall be arrested, charged, or convicted of
a violation of any [speeding ordinance] based on a peace officer’s unaided
visual estimation of the speed of a motor vehicle." Ohio Rev. Code
§ 4511.091(C)(1); see also 2011 Ohio Laws 29.
   The Ohio Legislature recognized, as a practical matter, that police offi-
cers can enforce traffic safety laws in a way that simultaneously safe-
guards our most fundamental constitutional rights. Because our
consideration here today concerns probable cause, we adhere to the tradi-
tional reasonableness standard which is far less restrictive than the per se
prohibition adopted by the Ohio legislature addressing the arrest, charging,
or conviction of an individual.
                   UNITED STATES v. SOWARDS                    25
can." Post at 26. But the irony, if any, of the dissent’s com-
parison is lost when one recognizes that lay persons do not
use their estimates to stop vehicles on public highways.
Because police officers do stop vehicles, their estimates must
satisfy the Fourth Amendment’s probable cause requirement.

   Next, the dissent contends that "the majority completely
invalidates the road test North Carolina has employed for its
traffic officers to demonstrate their ability to estimate the
speed of cars." Post at 52. Setting aside that it is wholly
unclear why such a policy consideration would have any rele-
vance to a Fourth Amendment probable cause analysis,
today’s majority opinion makes no such holding that invali-
dates North Carolina’s radar certification test for its intended
purpose: namely to instruct officers on the use of radar instru-
ments.

   The dissent further contends that today’s majority opinion
creates a "heightened evidentiary burden" for traffic stops
based solely on an officer’s estimate of a vehicle’s slight
speeding. Post at 27. However, Beck’s requirement that "rea-
sonably trustworthy information" must serve as the founda-
tion for probable cause dates to 1964, and, indeed, the Fourth
Amendment specifically protects persons against unreason-
able searches and seizures; we see nothing "heightened" in
requiring a police officer to have probable cause based on
"reasonably trustworthy information" prior to stopping a
motor vehicle for speeding. 379 U.S. at 91.

                               IV.

   For the foregoing reasons, we hold that the district court
erred in denying Sowards’s motion to suppress because Dep-
uty Elliott lacked probable cause to initiate a traffic stop based
exclusively on his uncorroborated and unsupported belief that
Sowards was traveling 75 mph in a 70-mph zone.

                               REVERSED AND REMANDED
26                 UNITED STATES v. SOWARDS
TRAXLER, Chief Judge, dissenting:

   Today, we establish that a police officer cannot legally stop
a speeding vehicle based only upon his visual estimate unless
the vehicle is traveling in "significant excess" of the speed
limit or the officer has the time and practical ability to con-
firm his belief that the vehicle is speeding through radar, pac-
ing, or some other corroborating evidence. No longer will the
officer’s professional judgment alone be adequate, and the
prohibition applies regardless of the extent of the officer’s
training, experience, or certified ability to accurately estimate
vehicle speeds within a very narrow margin of error. Ironi-
cally, while a lay person can estimate the speed of such a
vehicle based upon his or her personal observations, an expe-
rienced and trained police officer no longer can.

   Deputy Elliott has more than eight years of experience in
the daily enforcement of North Carolina’s traffic laws, and
has three times demonstrated through North Carolina’s radar
certification procedures an ability to accurately estimate the
speed of moving vehicles within an average 3.5-mph margin
of error. These facts are uncontradicted. Yet the majority
holds that Deputy Elliott’s visual estimate that Sowards’s
vehicle was traveling 5 mph over the posted speed limit is
inherently unreliable and, without corroborating evidence,
insufficient as a matter of law — not to sustain a conviction,
but rather to provide probable cause to stop the vehicle. In
doing so, the majority also effectively holds that North Caroli-
na’s certification test required to demonstrate an officer’s
ability to estimate the speed of vehicles, like similar programs
employed by a number of states across our country, is invalid
as a matter of law. Even though a motorist is speeding, knows
he is speeding, and may well admit that he is speeding if
stopped, an officer working alone and without radar cannot
even pull the car over for a warning as long as the driver is
reasonably believed to be only breaking the law slightly as
opposed to significantly — a distinction this circuit has never
made for unlawful behavior.
                      UNITED STATES v. SOWARDS                            27
   In adopting its inflexible corroboration requirement for
"slight" speeding violations, I believe the majority has unnec-
essarily distorted the well-established "totality of the circum-
stances" test normally applicable to all probable-cause
determinations, and has effectively required that an officer
have evidence sufficient for a jury to convict beyond a reason-
able doubt before he may stop the vehicle. And it does so
based upon its belief, mistaken in my view, that speeding vio-
lations present some kind of "unique circumstance" requiring
this heightened evidentiary burden. Because I cannot agree
with this unwarranted limitation on probable-cause jurispru-
dence, I respectfully dissent.

                                     I.

   Deputy Elliott is a ten-year veteran in law enforcement in
North Carolina, the last eight of which included as a regular
part of his duties "the enforcement of traffic laws, including
speeding." J.A. 20. After working three years in the patrol
division, he was selected for placement on the Governor’s
Highway Safety Program ("GHSP") highway interdiction
team.1 Deputy Elliott’s qualifications to visually estimate the
speed of vehicles, however, is not limited to his years of expe-
rience in speed enforcement. He also "received specialized
training as it relates to the enforcement of the traffic laws in
the state of North Carolina," J.A. 20, including "specialized
training in radar certification," J.A. 21.

   Deputy Elliott described in some detail the training and
testing involved in North Carolina’s certification process. As
a prerequisite, the certification candidate first trains with a
  1
    The Governor’s Highway Safety Program stems from a state-wide
grant designed to facilitate enforcement of North Carolina’s traffic laws on
the interstate systems and reduce the number of traffic crashes and fatali-
ties. In the course of traffic enforcement, the officers also enforce narcot-
ics and money laundering laws. See J.A. 20; North Carolina Department
of Transportation, Governor’s Highway Safety Program, http://
www.ncdot.org/programs/ghsp (last visited Mar. 31, 2012).
28                    UNITED STATES v. SOWARDS
certified operator who "show[s] you how to work the radar"
and "show[s] you how to estimate the speed[]" of vehicles.
J.A. 23. Although there is "not really a technique [to] measur-
ing speeds," J.A. 24, it is nonetheless a skill developed by
practice and experience. Indeed, in North Carolina, it is a crit-
ical one, as radar alone cannot support a conviction for speed-
ing as a matter of law. See State v. Jenkins, 342 S.E.2d 550,
552 (N.C. Ct. App. 1986) ("By the express provisions of
[North Carolina’s] statute, . . . the speed of a vehicle may not
be proved by the results of radar measurement alone and . . .
such evidence may be used only to corroborate the opinion of
a witness as to speed, which opinion is based upon actual
observation."); see also J.A. 78-79 (testimony of Deputy
Elliott confirming that "you cannot run a radar unit at all
unless you have a visual estimation" and that "[t]he radar unit
is only there to corroborate what you already know").

   After training, candidates must pass a written test and a
road-course test. To pass the road-course test, candidates
observe twelve vehicles, "estimate their speed, and then cor-
roborate [the] visual calculations with the use of [the] radar,"
all under the supervision of a certified instructor. J.A. 25.2 The
margin of error is a combined 42 mph, or an average of 3.5
mph per vehicle. However, the candidate will automatically
fail if he varies more than 12 mph on any single vehicle. Dep-
uty Elliott successfully passed the tests and received certifica-
tion in May 1998, April 2000, and February 2004. His
certification was current when he stopped Sowards.
  2
   Deputy Elliott testified that the instructor "cover[s] up the . . . radar
unit, the target speed. And then at that point in time you’re formulating
your opinion, you’re making a visual estimation. Once you make that
visual estimation, then you are allowed to run the radar. At that point in
time you make a clock with that radar. And once you confirm that that’s
what . . . has happened, that’s when the certified instructor takes . . . the
piece of paper off your radar unit and advises you what the actual clock
was." J.A. 25.
                      UNITED STATES v. SOWARDS                            29
   On April 11, 2006, Deputy Elliott positioned his vehicle in
the median of Interstate 77, pointed south so as to provide him
with an unobstructed view of approaching northbound traffic
and a tracking history of approximately 100 yards, or the
length of a football field. Deputy Elliott had been working
this specific stretch of I-77 on a daily basis for more than 4
years. The posted speed limit was 70 mph.3

   While so positioned, Deputy Elliott continuously observed
Sowards’s vehicle as it approached and passed him. He esti-
mated the vehicle’s speed to be 75 mph. After stopping the
vehicle, Deputy Elliott advised Sowards that he had been
stopped for traveling 75 mph and that he should be driving the
speed limit to be safe. Sowards does not contest that he was
speeding.

   Sowards presented Deputy Elliott with an Ohio driver’s
license and said that he had traveled from Ohio to Atlanta by
bus to pick up the car and return to Ohio. He claimed that his
girlfriend "Deanna" owned the vehicle, but that he "didn’t
really know her last name." J.A. 38. According to the registra-
tion, however, the vehicle belonged to "Retcha Daily" from
Georgia. J.A. 36. Due to the discrepancies, Deputy Elliott
contacted the Blue Lighting Operations Center ("BLOC") to
obtain additional information on the license and vehicle, and
advised Sowards that he would issue a warning ticket for
speeding if everything checked out. While waiting for the
response, Deputy Elliott observed that Sowards was sweating
profusely and had a pre-paid cellular phone, and Deputy
Elliott decided to have his drug dog perform an open-air sniff
of the exterior of the vehicle. The dog alerted at the trunk.
During the ensuing search, the officers detected the smell of
  3
    To obtain a reliable reading, the radar unit can be at no more than a 20-
degree angle. Deputy Elliott parked his car at a 25- to 30-degree angle
because on a previous occasion his car had almost been hit by a tire that
had come off a passing trailer. After that incident, Deputy Elliott posi-
tioned his car farther from the road and at the broader angle.
30                    UNITED STATES v. SOWARDS
laundry detergent, which is often used to mask the scent of
narcotics, and discovered a compartment containing 10 kilo-
grams of cocaine.

   Prior to pleading guilty to the resulting drug charges, Sow-
ards filed a motion to suppress the evidence obtained during
the search. Sowards argued that Deputy Elliott’s visual esti-
mate of his speed was insufficient to establish probable cause
to stop his vehicle and that the dog sniff occurred during a
period of unlawful detention.

   Deputy Elliott was the only witness who testified at the
suppression hearing and his testimony is uncontradicted.
Although lay witnesses may offer opinions as to speed esti-
mates, the district court found that Deputy Elliott’s "consider-
able training in estimating speeds" and the "foundation [laid]
to testify as a law enforcement officer trained in estimating
speeds" also qualified him as an expert. J.A. 31. At the con-
clusion of the hearing, the court denied the motion to sup-
press. With regard to the question of whether there was
probable cause to initially stop Sowards’s vehicle, the court
held as follows:

      [Deputy] Elliott had probable cause to believe a traf-
      fic violation had occurred based on speed. He’s
      trained to estimate speeds. His difficulty with mea-
      surements is immaterial to his estimate of speed as
      that did not depend on time or distance. And the cer-
      tification that he received . . . three times, depended
      on accuracy in estimating speeds. So he had a partic-
      ularized and objective basis for suspecting that a
      traffic violation had occurred.

J.A. 121.4 I would affirm.
  4
   During the hearing, Deputy Elliott had difficulty answering questions
regarding the measurements in feet and yards. The majority concludes that
the district court clearly erred in finding that this difficulty with small
                      UNITED STATES v. SOWARDS                            31
                                     II.

                                     A.

   The Fourth Amendment guarantees the right of persons to
be free from "unreasonable searches and seizures." U.S.
Const. amend. IV. A law enforcement officer’s decision to
stop a motorist constitutes a seizure within the Fourth Amend-
ment, see Whren v. United States, 517 U.S. 806, 809-10
(1996), and will be reasonable so long as the officer has
"probable cause to believe that a traffic violation has
occurred," id. at 810.

   Whether an officer has probable cause to believe that a traf-
fic offense has occurred is determined by the "totality of the
circumstances." Maryland v. Pringle, 540 U.S. 366, 371
(2003). We examine all events leading up to the stop and
decide "whether these historical facts, viewed from the stand-
point of an objectively reasonable police officer, amount to
probable cause." Id. (internal quotation marks omitted). In
doing so, we must also consider the officer’s practical experi-
ence and specialized training. Police may "draw on their own
experience and specialized training to make inferences from
and deductions about the cumulative information available to
them that might well elude an untrained person." United

measurements was immaterial to Deputy Elliott’s ability to estimate the
speed of Sowards’s vehicle, and in finding that Deputy Elliott was trained
to estimate speeds. For reasons discussed infra, I disagree. At the outset,
however, I am compelled to point out that the majority does not ultimately
reverse the district court based upon any perceived lack of confidence in
Deputy Elliott’s personal ability to offer a reliable opinion as to the speed
of Sowards’s vehicle. Rather, the majority reverses because Deputy
Elliott’s visual estimate fell within the slight-excess-of-the-speed-limit
category and was not corroborated by other evidence. At no point does
the majority explicitly indicate that the corroboration requirement was
triggered by a lack of confidence in Deputy Elliott personally, nor does it
expressly reverse the district court’s denial of the motion to suppress
based upon the district court’s findings of fact. See Majority Op. at 18-19.
32                    UNITED STATES v. SOWARDS
States v. Johnson, 599 F.3d 339, 343 (4th Cir. 2010) (internal
quotation marks omitted); see also United States v. Humph-
ries, 372 F.3d 653, 657 (4th Cir. 2004).

   Probable cause to stop a vehicle based upon a suspected
traffic violation exists when the facts and circumstances
within the officer’s knowledge are sufficient to warrant a pru-
dent person in believing that the suspect has committed a vio-
lation of a traffic law. See Michigan v. DeFillippo, 443 U.S.
31, 37 (1979). "The substance of all the definitions of proba-
ble cause is a reasonable ground for belief of guilt," but this
means far "less than evidence which would justify condemna-
tion or conviction," Brinegar v. United States, 338 U.S. 160,
175 (1949) (internal quotation marks omitted), and even less
than that required by the preponderance-of-the-evidence stan-
dard, see Illinois v. Gates, 462 U.S. 213, 235 (1983); Humph-
ries, 372 F.3d at 660. "[T]he probable-cause standard does not
[even] require that the officer’s belief be more likely true than
false." Humphries, 372 F.3d at 660; see also United States v.
Ortiz, 669 F.3d 439, 446 (4th Cir. 2012) ("A ‘reasonable
ground’ for belief [of guilt] is less demanding than a standard
requiring a preponderance of the evidence for the belief.");
United States v. Jones, 31 F.3d 1304, 1313 (4th Cir. 1994)
("The probable cause standard does not demand any showing
that such a belief be correct or more likely true than false."
(internal quotation marks omitted)).5
   5
     In its response to the dissent, the majority seizes upon my citation of
this latter portion of our established precedent comparing the probable-
cause standard to the preponderance standard to charge that I advance a
new "analytical approach" to probable-cause jurisprudence. Of course, this
is no analytical approach at all; it is a well-established holding designed
to ensure that police officers and courts do not conflate the probable-cause
standard with those requiring much more in the way of evidence—
specifically, the beyond-a-reasonable-doubt standard and the
preponderance-of-the-evidence standard. To the extent I emphasize this
portion of our precedent, it is because it is particularly apt in the case at
hand, in which the majority imports into our probable-cause inquiry a cor-
roboration requirement that originated in a handful of state court speeding
                      UNITED STATES v. SOWARDS                          33
                                    B.

   As the Tenth Circuit recently recognized, "[i]t’s long been
the case that an officer’s visual estimation can supply proba-
ble cause to support a traffic stop for speeding in appropriate
circumstances," and a radar reading or other such objective or
mechanical corroboration is not required. United States v.
Ludwig, 641 F.3d 1243, 1247 (10th Cir. 2011) (affirming dis-
trict court’s denial of motion to suppress illegal drugs found
in search of vehicle stopped for traveling 10 mph over the
speed limit); see also United States v. Pierce, 23 F.3d 404,
1994 WL 159767, at *2 (4th Cir. Apr. 28, 1994) (per curiam)
(affirming denial of motion to suppress where officer visually
estimated that vehicle was traveling 75 mph on interstate, but
was blocked from obtaining a radar reading by a tractor-
trailer); State v. Barnhill, 601 S.E.2d 215, 218 (N.C. Ct. App.
2004) (rejecting trial court’s requirement that an officer’s
visual estimate of speed must be corroborated by "objective
facts" or "objective criteria" as contrary to North Carolina
law, and noting that such a ruling "would have [had] the
effect of preventing an officer from stopping a vehicle based
solely upon the officer’s observations").

   In my opinion, the facts and circumstances known to Dep-
uty Elliott, coupled with his practical experience, training, and
the reasonable inferences drawn therefrom, were more than
sufficient to warrant an objectively reasonable belief on his
part that Sowards was speeding. Deputy Elliott is an experi-
enced officer who has been engaged in the enforcement of
traffic laws as a regular part of his duties for eight years. As
a part of his training, certification, and recertification, he has

conviction cases, discussed infra, based upon its view that "a speeding
violation presents a unique circumstance" necessitating evidence for prob-
able cause equivalent to that sufficient to sustain a conviction. Majority
Op. at 14 n.7. As I have clearly set forth above, probable cause does mean
something, but, even in traffic-stop cases, it surely does not mean "beyond
a reasonable doubt" or by "a preponderance of the evidence."
34                 UNITED STATES v. SOWARDS
demonstrated an uncontradicted ability to visually estimate
the speed of vehicles within an average margin of error of 3.5
mph per vehicle. He had worked this particular stretch of I-77
for over four years, at times in a position to corroborate his
visual estimates with radar; had become familiar with the
speed at which cars approached him; and had a clear, unob-
structed view of Sowards’s vehicle as it approached and
passed him.

   In a number of places, the majority takes issue with my rep-
resentation that North Carolina’s certification and training
procedures for police officers encompass both the officer’s
use of radar equipment and the officer’s ability to estimate
vehicle speeds within narrow margins of error. The majority
instead appears to believe that North Carolina’s procedures
are somehow limited to the use of radar equipment, and goes
so far as to state that the officer was merely "given the oppor-
tunity to ‘guess’ the speed of twelve vehicles" during his
training. Majority Op. at 10. However, the majority’s view
that the visual-estimate test is little more than an "opportunity
to guess," rather than a requirement to pass, is contradicted by
the record. The officers are instructed how to operate the par-
ticular radar equipment, but there is no basis upon which we
could conclude that the visual-estimate portion of the test is
somehow a less-crucial component or, worse, some form of
a guessing game. Deputy Elliott’s description of the training
and the requirements to pass the course is fully consistent
with what North Carolina law requires in order to obtain
speeding convictions. An officer’s visual estimate of the
speed of a vehicle is required to convict as a matter of law;
radar, assuming it is able to be used and is not excluded for
some reason, can only corroborate the officer’s observations.
Thus, to the extent we should pass judgment upon North Car-
olina’s training and certification program, I am confident that
North Carolina law enforcement would have the most interest
in ensuring that their officers are trained in and develop the
actual skill of accurately estimating the speed of vehicles in
case radar equipment is unavailable, blocked by other vehi-
                   UNITED STATES v. SOWARDS                    35
cles or obstructions, or is otherwise excluded for lack of cali-
bration or other deficiencies.

   Under these uncontradicted facts, which in any event we
must construe in the light most favorable to the government,
see United States v. Seidman, 156 F.3d 542, 547 (4th Cir.
1998), I believe the government has easily established that
Deputy Elliott had an objectively reasonable belief that Sow-
ards was speeding and, therefore, that he had probable cause
to stop Sowards’s vehicle for the suspected violation.

            III. The Corroboration Requirement

   The majority opines that "the Fourth Amendment does not
allow, and the case law does not support, blanket approval for
the proposition that an officer’s visual speed estimate, in and
of itself, will always suffice as a basis for an officer’s proba-
ble cause to initiate the traffic stop." Majority Op. at 14
(emphasis added). I agree. Such an inflexible rule would
ignore the totality-of-the-circumstances test and, in particular,
the mandate that we evaluate reasonableness based upon all
of the facts which led to the stop, including the officer’s train-
ing and experience. I disagree, however, with the majority’s
equally inflexible rule that an officer’s visual speed estimate
can never alone suffice as probable cause to stop a vehicle
that the officer estimates to be traveling only in "slight
excess" of the speed limit. Majority Op. at 14.

   The majority’s holding is clear: "[T]he reasonableness of
an officer’s visual speed estimate depends, in the first
instance, on whether a vehicle’s speed is estimated to be in
significant excess or slight excess of the legal speed limit."
Majority Op. at 14 (emphasis added). Where the officer visu-
ally estimates that a vehicle is traveling "in significant excess
of the legal speed limit," a visual estimate may "provide suffi-
cient ‘indicia of reliability’ to support an officer’s probable
cause." Majority Op. at 15 (emphasis added). But if the offi-
cer estimates that a vehicle is traveling only in "slight excess"
36                 UNITED STATES v. SOWARDS
of the speed limit, that estimate alone can never be enough;
the "officer’s visual speed estimate requires additional indicia
of reliability to support probable cause." Majority Op. at 16
(emphasis added); see also Majority Op. at 14 ("If slight, then
additional indicia of reliability are necessary to support the
reasonableness of the officer’s visual estimate." (emphasis
added)).

   A "slight excess" of the speed limit is defined only as a
"speed differential difficult for the naked eye to discern,"
Majority Op. at 16, or perhaps one that is otherwise believed
to be beyond the abilities of humans to accurately determine,
see Majority Op. at 19-20 (agreeing that "‘the accuracy of
human estimation of speed cannot easily, readily and accu-
rately discriminate between such small variations in speed’")
(quoting State v. Kimes, 234 S.W.3d 584, 588 (Mo. Ct. App.
2007)). Accordingly, the corroboration rule fashioned by the
majority applies regardless of the extent of any officer’s expe-
rience, specialized training, or demonstrated ability to accu-
rately estimate vehicle speeds within a narrow margin of
error. For the reasons set forth below, I do not think we
should impose this threshold inquiry upon the normal
probable-cause determination and hinge upon it an inflexible
requirement of corroboration every time a police officer stops
a vehicle for speeding in "slight excess" of the speed limit.

                               A.

   At the outset, I find the threshold inquiry, and the basis for
the significant/slight distinction used to trigger the
corroborative-evidence requirement, to be unsupported by the
record in this case and unworkable for police officers.

  Courts routinely allowed lay witnesses, with no training or
experience, to offer opinion testimony of their estimate of
speed provided they have had a sufficient opportunity to
observe the moving vehicle. And so long as that ability to
observe is established, I have found no opinion restricting the
                      UNITED STATES v. SOWARDS                            37
reliability or admissibility of the opinion testimony based
upon the time/distance mathematical formula for speed.6 Yet,
under the majority’s decision, a police officer’s identical
opinion will be deemed unreliable as a matter of law and,
therefore, insufficient to establish probable cause to believe
that a violation has occurred, unless the officer also estimates
the speed differential to have been a "significant" one.7
  6
     See State v. Barnhill, 601 S.E.2d 215, 217, 218 (N.C. Ct. App. 2004)
(noting "well established [rule], that any person of ordinary intelligence,
who had a reasonable opportunity to observe a vehicle in motion and
judge its speed may testify as to his estimation of the speed of that vehi-
cle," and that "it is not necessary that an officer have specialized training
to be able to visually estimate the speed of a vehicle"); Walker v. State,
295 S.E.2d 574, 575 (Ga. Ct. App. 1982) (allowing lay witness’s testi-
mony as to speed of a vehicle to support vehicular homicide conviction);
see also Asplundh Mfg. Div. v. Benton Harbor Eng’g, 57 F.3d 1190, 1197
(3d Cir. 1995) (noting that one example "of quintessential Rule 701 opin-
ion testimony [is] . . . the speed of a vehicle (footnote omitted)); Fed. R.
Evid. 701 advisory committee’s note (citing Asplundh for examples of
opinion testimony by lay witnesses); United States v. Conn, 297 F.3d 548,
554 n.2 (7th Cir. 2002) (same); State v. McLean, 16 A.3d 332, 343 (N.J.
2011) ("Traditional examples of permissible lay opinions include the
speed at which a vehicle was traveling."); Pierson v. Frederickson, 245
A.2d 524, 527 (N.J. Super. Ct. App. Div. 1968) ("It is clear that based on
adequate visual observation an ordinary witness can state his conclusion
of whether a car was moving fast or slow or give an estimate of its
speed."); State v. Clayton, 158 S.E.2d 557, 561 (N.C. 1968) ("Absolute
accuracy . . . is not required to make a witness competent to testify as to
speed.").
   7
     Although the majority denies that it has created a heightened evidenti-
ary burden for probable-cause in speeding cases, it sees no irony in the
fact that there will now be two different standards governing the use of
opinion testimony as to the speed of a vehicle — one for lay witnesses and
another for law enforcement officers. My colleagues justify this difference
by pointing out that a police officer uses his opinion as probable cause to
stop and detain motorists. To this I would simply point out that the opin-
ion of a lay person as to speed, admissible to support a criminal convic-
tion, should surely be sufficient to establish probable cause. Cf. Barnhill,
601 S.E.2d at 232 ("[I]f an ordinary citizen can estimate the speed of a
vehicle, so can Officer Malone.")
38                 UNITED STATES v. SOWARDS
   Additionally, the majority provides no clear numerical or
percentage division between driving in "slight excess" or "sig-
nificant excess" of the speed limit. The majority explains that
a "slight excess" is "a speed differential difficult for the naked
eye to discern," Majority Op. at 16, and ultimately declares
that no human could accurately estimate a 5-mph variation of
speed at 70-75 mph, see Majority Op. at 19-20 (citing Kimes,
234 S.W.3d at 589). However, there are no studies, expert tes-
timony, or other evidence to support this conclusion or to
enlighten law enforcement officers as to what speeding viola-
tion should be considered "slight" because it falls within that
which is difficult for the naked eye to discern or otherwise
beyond the capabilities of human estimation. Nor is there evi-
dence to support the majority’s finding that uncorroborated,
visual estimates of speeds in the "slight" category must be
presumed to be unreliable for purposes of the probable-cause
determination.

   As support for its holding that the officer’s visual estimate
of speed is inherently unreliable, the majority instead relies
upon "common sense," along with two cases involving anony-
mous tips, which we have held require additional corrobora-
tion or indicia of reliability. See United States v. Massenburg,
654 F.3d 480, 486 (4th Cir. 2011); United States v. Reaves,
512 F.3d 123, 126 (4th Cir. 2008). In this case, however, the
evidence consists not of hearsay statements of anonymous
witnesses regarding unlawful behavior, but rather the personal
observation and resulting opinion of a trained and certified
police officer, which the majority concludes is "inherently
unreliable" based upon nothing more than its own view,
unsupported by any evidence and contradicted by that which
was presented, that such estimates are beyond the capabilities
of any human being.

   Deputy Elliott demonstrated an actual ability to visually
estimate the speed of vehicles within an average, 3.5-mph
margin of error, in accordance with the requirements for radar
certification in North Carolina. And however remarkable one
                      UNITED STATES v. SOWARDS                          39
might believe this skill to be at first blush, it appears to be a
common one among experienced traffic officers across the
United States. See e.g., State v. Carter, No. 2CA-CR2008-
0013, 2009 WL 1717812, at *3 (Ariz. Ct. App. June 18, 2009)
(noting testimony that officer had completed a radar certifica-
tion class which required officers to accurately estimate the
speed of moving vehicles within 5 mph); State v. Estes, 223
P.3d 287, 288 (Idaho Ct. App. 2009) (noting that the officer
"had been trained in visually estimating the speed of vehicles
and had received certification of the ability to make estimates
within 5 miles per hour of the actual speed"); State v. McPart-
land, 36 A.3d 881, 887 n.5 (Me. 2012) (Jabar, J., dissenting)
(noting officer’s testimony that, as part of her radar training
course, "she was trained and certified to make visual esti-
mates of speed ‘within five miles per hour’"); State v. Ali, 679
N.W.2d 359, 368 (Minn. Ct. App. 2004) (noting that officer
had been "trained . . . to accurately estimate the speed of a
moving vehicle within five mph"); Barberton v. Jenney, 929
N.E.2d 1047, 1049 (Ohio 2010) (noting that, in order to be
certified under Ohio’s requirements, the officer "was required
to show that he could visually estimate a vehicle’s speed to
within three to four miles per hour of the vehicle’s actual
speed"); State v. Singh, No. F-98-022, 1999 WL 355270, at *1
(Ohio Ct. App. 1999) (noting trooper’s testimony that he had
been trained to visually estimate the speed of vehicles and
was generally accurate within one or two miles per hour);
Columbia County v. Kassens, 795 N.W.2d 492, 2011 WL
102598, at *1 (Wisc. Ct. App. Jan. 13, 2011) (noting officer’s
testimony that he "ha[d] been trained to visually estimate a
vehicle’s speed within three miles per hour").8
   8
     The majority agrees that no evidence exists to support its view of the
capabilities of human beings, but asserts that an evidentiary foundation is
unnecessary because it is "common sense" that no human can accurately
discriminate between such small variations of speed. In my view, the
majority’s conclusion concerning the limits of the abilities of trained
police officers falls well outside the realm of "common sense" and clearly
within the category of a factual finding necessitating evidentiary support.
40                    UNITED STATES v. SOWARDS
   In sum, I do not find the majority’s observations regarding
the capabilities of law enforcement officers to be supported
by the record. Moreover, I question how law enforcement
officers, particularly those who have met their state certifica-
tion requirements for visually estimating the speeds of vehi-
cles within narrow margins of error, will know when they
must forego stopping a speeding vehicle unless and until they
observe the vehicle cross into the "significantly speeding" cat-
egory or they are able to obtain other, corroborating evidence.

                                    B.

   Beyond these problems, I believe that the majority’s adop-
tion of the corroboration requirement for slight speeding vio-
lations has no place in the probable-cause context. The origin
of this new requirement is a handful of state court conviction
cases which have held or implied that a police officer’s visual
estimate of speed, standing alone, may not constitute suffi-
cient evidence to prove a defendant guilty beyond a reason-
able doubt if the variance between the visually estimated
speed and the speed limit is determined to have been "slight"
as opposed to "wide." State v. Kimes, 234 S.W.3d 584, 588
(Mo. Ct. App. 2007) (internal quotation marks omitted); City
of Kansas City v. Oxley, 579 S.W.2d 113, 116 (Mo. 1979);
see also State v. Estes, 223 P.3d 287, 289-91 (Idaho Ct. App.
2009); People v. Olsen, 239 N.E.2d 354, 355 (N.Y. 1968).9

Further, I do not see how we can make such a factual finding in the
absence of supporting evidence. Regardless of one’s view as to when logic
and common sense may be relied upon in the absence of actual evidence
of a particular fact, there is no absence of evidence in this case. Instead,
the only evidence in the record contradicts the majority’s finding. The evi-
dence of Sowards’s actual, demonstrated ability to accurately discriminate
between speeds within a 3.5-mph margin of error during three separate
tests was unchallenged by Sowards below, and cases from across the
country show that many police officers are similarly trained in visually
estimating speeds within such narrow margins of error.
   9
     In Kimes, the Missouri Court of Appeals affirmed a speeding convic-
tion based upon a 15-mph differential (a 75% variance) because it was
                      UNITED STATES v. SOWARDS                            41
   To date, our circuit has not adopted a corroboration rule in
conviction cases. See e.g., United States v. Daras, 164 F.3d
626, 1998 WL 726748, at *2 (4th Cir. Oct. 16, 1998) (per
curiam) (noting that "the Government correctly points out that
the officer’s visual estimate is also sufficient, by itself, to sup-
port a conviction"); see also United States v. Wornom, 754 F.
Supp. 517, 519 (W.D. Va. 1991) (affirming conviction based
upon an officer’s visual estimate where radar evidence was

deemed "not slight." In doing so, it was compelled to distinguish the ear-
lier Missouri Supreme Court opinion in Oxley, which had reversed a
speeding conviction based upon a 10-mph differential (a 29% variance).
By way of example, the Kimes court made a number of unsupported
assumptions:
    Where an officer’s estimation of speed is 60 m.p.h., a fact-finder
    cannot conclude with any degree of certainty that a defendant
    was exceeding a 55 m.p.h. speed limit, because the accuracy of
    human estimation of speed cannot easily, readily, and accurately
    discriminate between such small variations in speed. Yet the
    same fact-finder, based upon that same 60 m.p.h. estimation of
    speed, could conclude beyond a reasonable doubt that a defen-
    dant was exceeding a 20 m.p.h limit. This is so because the vari-
    ance between the estimated speed and the speed limit falls within
    the margin of error of accuracy within which an experienced per-
    son can discriminate between the two speeds.
Kimes, 234 S.W.3d at 589 (emphasis added). In support of Kimes’ blanket
statement regarding human capabilities (with which the majority here
agrees), Kimes also cites no studies, expert testimony, or other evidence.
However, there is also no indication that the officers in Oxley or Kimes
had developed or demonstrated any specialized ability to estimate the
speed of vehicles. In my view, the finding regarding human abilities
adopted by the majority is directly contradicted by the only evidence that
was presented on the point in this case, as well as by observations to the
contrary made by many other courts throughout the country. It appears
that police officers work and train to develop this ability, and become very
adept at estimating speeds within quite narrow margins of error. See also
City of Rockford v. Custer, 936 N.E.2d 773, 776-77 (Ill. Ct. App. 2010)
(discussing this line of speeding-conviction cases but indicating that a con-
viction might still be affirmed where the officer gives a visual estimate of
the defendant’s actual speed that falls within the appropriate margin of
error).
42                    UNITED STATES v. SOWARDS
suppressed). In my view, such matters should ordinarily be
left for the jury or other factfinder to consider and weigh.10

   But even if we had seen fit to require corroboration in con-
viction cases involving a slight speed differential, I do not
think it prudent to import this reasoning into the probable-
cause context and superimpose an inflexible corroboration
requirement upon the totality-of-the-circumstances test. "The
Supreme Court has repeatedly admonished that the standard
for probable cause is not ‘finely tuned’ or capable of ‘precise
definition or quantification into percentages.’" Humphries,
372 F.3d at 660. Rather, the officer need only have an objec-
tively reasonable belief that the defendant is speeding, and
that belief need not even "be more likely true than false." Id.

   Thus, even in those states that have required more than just
the officer’s visual observation to sustain a conviction for
speeding where there is a "slight variance," the courts have
pointed out the important distinction between the evidence
   10
      Other state courts have also expressed similar views in the conviction
context. See e.g., Ferguson v. State, 587 S.E.2d 195, 196 (Ga. Ct. App.
2003) (holding that an officer’s visual estimation of a vehicle’s speed is
sufficient to support a conviction for speeding); Jackson v. State, 477
S.E.2d 28, 29 (Ga. Ct. App. 1996) (affirming conviction for speeding
based solely upon the officer’s visual speed estimate, and noting that
"opinion testimony of an eyewitness may be used to establish speed, its
credibility being for the jury to determine" (citation and alterations omit-
ted)); State v. Ali, 679 N.W.2d 359, 368 (Minn. Ct. App. 2004) (holding
that trained officer’s visual estimate that defendant was traveling 11 mph
above the speed limit was sufficient by itself to support a conviction for
speeding); Barberton v. Jenny, 929 N.E.2d 1047, 1049, 1051 (Ohio 2010)
(rejecting "a bright line rule that an officer’s visual estimation of speed,
without other evidence to support it, is insufficient to sustain a conviction
for speeding" and "hold[ing] that a police officer’s unaided visual estima-
tion of a vehicle’s speed is sufficient evidence to support a conviction for
speeding . . . without independent verification of the vehicle’s speed if the
officer is trained [and] certified by [an] organization that develops and
implements training programs to meet the needs of law-enforcement pro-
fessionals and the communities they serve, and is experienced in visually
estimating vehicle speed").
                   UNITED STATES v. SOWARDS                  43
needed to establish probable cause and that needed to sustain
a conviction. Of particular note, in State v. Ostdiek, 351
S.W.3d 758, 768-69 & 769 n.10 (Mo. Ct. App 2011), the Mis-
souri Court of Appeals, citing its earlier opinion in Kimes,
recently reversed a defendant’s speeding conviction based
solely upon the officer’s testimony that it "just appeared" that
the vehicle was going faster than her vehicle and the others
on the road. However, the court took care to point out that
"[t]he reversal of the speeding conviction does not affect the
legitimacy of the initial traffic stop or any evidence which
resulted from that stop," the latter of which implicates a much
different standard of review than the "beyond a reasonable
doubt" determination necessary for a conviction. Id. at 769
n.10; see also Estes, 223 P.2d at 289 n.1 (noting that the issue
of whether an officer’s visual estimate of a vehicle’s speed
constitutes sufficient proof of speed beyond a reasonable
doubt to sustain a conviction "should not be confused with the
admissibility of an officer’s estimate of speed nor with the
sufficiency of an estimate to provide reasonable suspicion to
stop a vehicle, reasonable suspicion being a much less exact-
ing standard than proof beyond a reasonable doubt" (emphasis
omitted)). Thus, it appears that even the state courts in Mis-
souri and Idaho would not import their corroboration require-
ment for "slight variance" speeding convictions into the
probable-cause context.

                              C.

   Finally, I turn to the two unpublished "probable cause"
cases cited by the majority in support of its holding: United
States v. Moore, No. 10cr971(RJH), 2011 WL 6325973
(S.D.N.Y. Dec. 19, 2011), and State v. Petzoldt, 803 N.W.2d
128, 2011 WL 2556961 (Iowa Ct. App. June 29, 2011). Both
involve a court’s determination that an officer’s visual speed
estimate was insufficient to establish probable cause to stop
a vehicle under the totality of the circumstances, but neither
counsels our adoption of an absolute rule requiring corrobo-
rating evidence to establish probable cause in every case
44                 UNITED STATES v. SOWARDS
where the officer observes a slight violation of the legal speed
limit.

   In Moore, the two officers involved were anti-crime offi-
cers whose primary duties were "to respond to violent felonies
rather than to enforce traffic laws." Moore, 2011 WL
6325973, at *1. The first officer testified that the vehicle in
question was "traveling in excess of the speed limit," but he
"did not describe how much experience he had had conduct-
ing traffic stops or estimating the speeds of traveling cars." Id.
at *2 (internal quotation marks omitted). The second officer
likewise "did not describe his experience in enforcing speed-
ing violations or in identifying the speed of vehicles by sight."
Id. at *3. Although noting that courts "will credit the observa-
tions of officers that a car was speeding when the officer has
had special training [and experience] in detecting the speeds
of vehicles," id. at *5, the district court found no such founda-
tion for the officer’s opinion in its case:

        By contrast, here, there is no suggestion that the
     officers have received any such training. Moreover,
     nothing about the officers’ experience — nor their
     assigned duties on the night in question — suggests
     that they would have had the opportunity to become
     adept at estimating the speeds of vehicles. It seems
     likely that some police officers — such as state
     troopers who, as part of their regular duties, rou-
     tinely estimate how fast particular cars are driving
     and test such an estimate by using a radar gun —
     might become very adept at judging a car’s speed.
     Here, however, the Court has no such reason for
     confidence, based on the officers’ training or experi-
     ence . . . , in the officer’s estimation — an "estima-
     tion," the Court notes, that hardly qualifies as such,
     given the vagueness of the officers’ responses and
     their inability to give even a range of speeds at
     which the cab might have been traveling. The offi-
     cers did not state that they had received specialized
                   UNITED STATES v. SOWARDS                   45
    training in estimating the speed of moving vehicles,
    nor did they state that they had previously . . .
    worked an assignment where their main responsibil-
    ity was to apprehend violators of traffic laws. The
    officers both stated that on the night in issue, they
    were assigned to the Bronx Anti-Crime Unit, whose
    mission is not to enforce the Vehicle and Traffic
    Laws, but rather to focus on violent felonies. The
    officers were not even carrying books of summonses
    to issue in the event that they observed a traffic
    infraction.

Id. a *6. Thus, the Moore officers had no training or demon-
strated ability to estimate the speed of vehicles, had no experi-
ence doing so, and offered no opinion as to the speed
differential at all.

   The majority’s reliance upon Petzoldt is similarly mis-
placed. In Petzoldt, the officer had "resorted to playing Soli-
taire on his computer to break the monotony of a very slow
night" when "the stillness was broken [by] a pickup truck"
passing by his location. Petzoldt, 2011 WL 2556961, at *1.
"Believing the truck was speeding," the officer pursued the
vehicle. Id. As in Moore, the court held that "with proper
foundation, an officer’s visual estimation of speed may be
sufficient to supply probable cause to stop a vehicle for speed-
ing." Id. at *3. It did not, however, adopt a corroboration
requirement based upon the degree of the estimated speed dif-
ferential. Rather, it reversed the trial court’s denial of defen-
dant’s motion to suppress because the officer did not have the
requisite foundation for his opinion:

       Here, Officer King testified he was playing Soli-
    taire when he observed Petzoldt’s pickup truck
    briefly as it passed in front of his patrol car.
    Although he testified he believed the truck was
    [speeding], Officer King made no estimate as to how
    fast the truck was travelling or how much over the
46                 UNITED STATES v. SOWARDS
     posted limit he thought [it] was travelling. The
     posted speed limit is not even in the record before
     us. Officer King’s visual estimate of speed was not
     confirmed by any other means of corroboration of
     the speed, such as radar or pacing. Officer King
     observed no other traffic infractions or driving ano-
     malies by the pickup.

Id. (footnotes omitted). Thus, the Petzoldt officer had no
tracking history, had no training or demonstrated ability to
visually estimate the speed of vehicles, and made no estimate
of the speed differential.

   Neither Moore nor Petzoldt support adoption of an absolute
requirement for corroborating evidence in the probable-cause
context where an experienced traffic officer has visually esti-
mated the speed of a vehicle to be in only "slight excess" of
the speed limit. The contrast between Deputy Elliott and the
officers involved in Moore and Petzoldt could not be more
stark. Deputy Elliott was trained and certified in radar
enforcement, experienced in traffic enforcement, and had
demonstrated through certification and testing procedures his
adeptness at judging the speed of vehicles. His testimony was
specific, both as to his estimate and as to the speed limit, and
he had a continuous and unobstructed view of Sowards’s
vehicle as it approached him. The facts of this case are simply
not analogous.

                              D.

   To summarize, neither the state-court conviction cases nor
the unpublished probable-cause cases relied upon by the
majority support its broad holding that an officer’s visual
speed estimate can never suffice as a basis for an officer’s
probable cause to initiate a traffic stop unless the suspect is
estimated to be traveling in significant excess of the speed
limit or the officer has the time and ability to corroborate his
visual estimate through some other objective technique or cir-
                   UNITED STATES v. SOWARDS                   47
cumstance. And the majority’s apparent basis for the rule—
that "‘the accuracy of human estimation of speed cannot eas-
ily, readily, and accurately discriminate between such small
variations in speed," Majority Op. at 19-20 (internal quotation
marks omitted)—is not supported by the evidence in this case,
which we must view in the light most favorable to the govern-
ment.

   In my opinion, an experienced officer such as Deputy
Elliott, who has demonstrated an ability to estimate speed
within a 3.5-mph margin of error, has all of the qualifications
needed to form a reasonable belief that a speeding violation
of 5 mph or more has occurred. Under today’s holding, how-
ever, such an experienced, trained and certified police officer
cannot legally stop a vehicle that he legitimately and reason-
ably believes is traveling in "slight excess" of the speed limit
and posing a potential threat to others based solely upon his
visual estimate and professional opinion. I do not believe our
probable-cause jurisprudence, which requires no more than
that a law enforcement officer have such a reasonable belief,
counsels or even permits that result.

                    IV.   Factual Findings

                               A.

   I turn now to the majority’s conclusion that the district
court clearly erred in finding that Deputy Elliott "is trained to
estimate speeds" and that "[h]is difficulty with measurements
is immaterial to his estimate of speed as they did not depend
on time or distance." J.A. 121. As noted earlier, these factual
findings, whether "clearly erroneous" or not, do not serve as
the basis for the majority’s decision. No explanation is ever
given by the majority to show how the rejection of the district
court’s factual findings factors into the ultimate holding in the
case. See Majority Op. at 19-20. But no explanation probably
needs to be given, as the corroboration requirement alone is
all that the majority needs to reverse the district court as a
48                 UNITED STATES v. SOWARDS
matter of law. Although I strive to find otherwise, the majori-
ty’s holding seems clear to me: as a matter of law, a police
officer can never premise probable cause solely on his or her
visual estimate of speed if the speed differential is "slight" as
opposed to "significant"—no matter the officer’s training,
knowledge, experience, certification, or demonstrated ability
to estimate speeds or recite measurements. And this is
because the majority "agree[s] that ‘the accuracy of human
estimation of speed cannot easily, readily, and accurately dis-
criminate between such small variations in speed.’" Majority
Op. at 19-20 (quoting Kimes, 234 S.W.2d at 589). Thus, it
matters not at all to the result whether Deputy Elliott was
"trained" to visually estimate speed, as opposed to having
developed and demonstrated the skill to do so during his train-
ing and certification, nor is there any indication that the result
in this case would have been any different if Deputy Elliott
had correctly recited the lengths of rulers and yardsticks.

   In sum, Sowards’s difficulties with measurements—no
matter how silly they seem or what fodder they would have
made for cross-examination at trial — are irrelevant to the
rule adopted today, and the district court’s factual findings,
whether clearly erroneous or not, are not relevant to the legal
determination that troubles me most.

                               B.

   Had the majority relied upon Deputy Elliott’s lack of suffi-
cient training or his inability to accurately recite measure-
ments as a basis for determining that his visual estimate was
unreliable, and therefore in need of corroboration, my dissent
would remain. But it would rest on a much narrower basis: I
disagree with the majority’s conclusion that the district court
clearly erred in finding that Deputy Elliott was "trained to
estimate speeds" and that his "difficulty with measurements
[was] immaterial to his estimate of speed [because] they did
not depend on time or distance." J.A. 121.
                   UNITED STATES v. SOWARDS                  49
   Under the clear-error standard, "[a] factual finding by the
district court may be reversed only if, although there is evi-
dence to support it, the reviewing court on the entire evidence
is left with the definite and firm conviction that a mistake has
been committed." Walton v. Johnson, 440 F.3d 160, 173-74
(4th Cir. 2006) (en banc) (internal quotation marks omitted).
"Where there are two permissible views of the evidence, the
factfinder’s choice between them cannot be clearly errone-
ous." Walker v. Kelly, 589 F.3d 127, 141 (4th Cir. 2009)
(internal quotation marks omitted).

   First, Deputy Elliott’s uncontradicted testimony is that he
was required, as a part of his preparation for radar certifica-
tion in North Carolina, to work with a certified instructor who
"show[ed] [him] how to estimate the speeds" of vehicles. J.A.
23. That sounds like training to me. I do not know what else
it could mean. At the conclusion of the course, Deputy Elliott
was also required to demonstrate to his instructor the ability
to accurately estimate speeds within an average 3.5-mph mar-
gin of error. In my view, the district court’s choice of words
— that Deputy Elliott was "trained to estimate speeds" — is
accurate.

   Second, Deputy Elliott inexplicably became confused when
he was questioned about the measurements of feet and yards.
He may well not know the correct answers to those questions,
or he may just have had difficulty quickly recalling or con-
verting such measurements on the witness stand. Unlike
VASCAR, however, which involves a distance determination
and timing mechanism to approximate speed according to the
time/distance formula, there is no evidence that the reliability
of an officer’s visual estimation of speed is or should be tied
to a specific or minimum distance or time. See McBee v.
State, 673 S.E.2d 569, 571 (Ga. Ct. App. 2009) (rejecting
defendant’s argument that his motion to suppress should have
been granted based upon the officer’s "failure to use mathe-
matical calculations or radar to estimate [the vehicle’s] speed"
because "an officer’s visual estimate may be used to establish
50                     UNITED STATES v. SOWARDS
speed"); Barberton, 929 N.E.2d at 1051 ("Visual observation
has long been held a valid means of determining the speed of
a moving vehicle as long as the witness has a reliable oppor-
tunity to view the vehicle." (internal quotation marks omit-
ted)). There was likewise no evidence that North Carolina’s
certification procedure for estimating speeds is dependent
upon distance or time.

   In my view, conditioning the materiality of a visual esti-
mate of speed on the existence of a mathematical calculation
ignores the realities of traffic enforcement and unduly ties the
hands of officers who must have the freedom to exercise their
judgment. Indeed, as a practical matter, it seems likely that
visual estimates would perhaps most often come into play
where police officers observe a speeding vehicle while
engaged in their routine patrol duties and not while positioned
where they can check speeds utilizing a time/distance mathe-
matical calculation.11
  11
     The majority additionally charges that the district court’s finding
"rings in the absurd," because no one can "discern the speed of a vehicle
. . . without discerning both the increment of distance travelled and the
increment of time passed." Majority Op. at 11-12. To answer the majori-
ty’s question, I do not quibble with the mathematical formula for speed,
and express no opinion as to whether we should take judicial notice of it.
However, I do disagree with the majority’s holding that witnesses cannot
offer an estimate of speed without knowing precisely the distance traveled
and time elapsed. This is not a classroom or a laboratory, nor are the roads
upon which police officers patrol. District courts are often called upon to
make determinations as to a witness’s ability to offer opinion testimony,
based upon the witness’s personal observations. Estimates of speed fall
squarely and historically within the realm of opinion testimony that may
be received even from lay witnesses, and which fall within the province
of the factfinder (be that the district court or a jury) to evaluate and weigh.
Credibility determinations must be made, which likewise rest with the
factfinder and not with us.
   In sum, a lay witness’s estimation of speed, as opposed to an expert’s
mathematical calculation of speed, is not tied to distance or time, or con-
tingent upon a mathematical formula, when offered in a court of law, and
the majority points to no case in which it has been. It is instead tied to the
                       UNITED STATES v. SOWARDS                            51
   Finally, and to the extent the majority’s determination on
this factual finding or its holding at all rests upon Deputy
Elliott’s personal competency, I note that whatever difficulties
Deputy Elliott might have had in recalling the measurements
of feet and yards while being questioned in a courtroom, these
difficulties have not prevented him from passing the certifica-
tion tests nor prevented him from accurately determining the
speed of moving vehicles while on the street and engaged in
his normal law enforcement duties.

   The uncontradicted evidence in this case demonstrates that
Deputy Elliott’s ability to estimate vehicle speeds was based
upon his experience, training, and opportunity to observe the
vehicle as it approached and passed him, rather than upon a
known distance or minimum time. In my view, the evidence
was more than sufficient to provide a foundation for his opin-
ion in this case and to support his objectively reasonable
belief that Sowards was speeding. For the same reasons, I am
not left with a definite and firm conviction that the district
judge, who had the opportunity to observe Deputy Elliott,
made a mistake in finding that Deputy Elliott’s testimony
regarding small measurements was immaterial to his estimate
of the speed of Sowards’s vehicle, or in concluding that Dep-
uty Elliott had probable cause to stop him.

                                     V.

   In my opinion, the majority’s decision today strikes a blow
to the professional judgment of police officers, substitutes our
opinion regarding the ability of officers to accurately assess

"witness’s perception," and, in particular, his fair opportunity to personally
observe the moving object. See e.g. Fed. R. Evid. 701. It is an estimate,
not "a guess," based upon the witness’s personal observation, and the type
of opinion evidence routinely received by courts. When evaluated in the
context of probable cause, it is further evaluated with reference to the
training and experience of the police officer, which, as it happens in this
case, was quite substantial.
52                 UNITED STATES v. SOWARDS
the speed of vehicles for the facts presented, and severely ties
the hands of trained and experienced police officers to enforce
traffic safety laws. Whether, and to what extent, we might
require corroborating evidence for slight speed differentials
for purposes of sustaining a conviction should remain for
another day. Whether visual estimates of speed within a slight
speed differential are sufficiently reliable to prove that a vehi-
cle was speeding "by a preponderance of the evidence" in the
civil context is likewise not before us today. For purposes of
the probable-cause determination, the officer need only have
a "reasonable ground for belief of guilt." Brinegar, 338 U.S.
at 175 (internal quotation marks omitted), which need not
even "be more likely true than false," Humphries, 372 F.3d at
660.

   Additionally, the majority completely invalidates the road
test North Carolina has employed for its traffic officers to
demonstrate their ability to estimate the speed of cars. From
pages 20 to 23 of the majority opinion, my colleagues give
their reasons for finding the test inadequate to demonstrate an
officer’s expertise to judge speed without the use of radar.
Although my colleagues summarily deny that they have taken
this step, they nonetheless set forth in some detail the per-
ceived "shortcomings" of North Carolina’s test for the pur-
pose of discrediting Deputy Elliott’s demonstrated abilities in
this area and rendering his opinion, and all others like it, unre-
liable as a matter of law. Majority Op. at 22. Consequently,
it seems clear to me that trained and certified police officers
can no longer stop a speeding vehicle based only on their
visual speed estimates unless satisfied that the vehicle falls
within the as yet undefined "significant speeding" category.
Given that it is only such "significant" speed differentials that
do not require corroboration or other indicia of reliability
under the majority’s holding, I can only view this as a whole-
sale rejection of North Carolina’s testing and visual-estimate
certification procedures as they would apply to "slight" speed-
ing violations. Yet the certification procedure was never chal-
lenged below or on appeal, and there is no evidence to support
                       UNITED STATES v. SOWARDS                             53
its invalidation. There is no telling what the ramifications will
be in North Carolina and the other states of our circuit now
that this certification procedure has been found insufficient.12

  Based upon his substantial training, experience, multiple
certifications, and personal observations, Deputy Elliott had
an objectively reasonable belief that Sowards was speeding,
and thus had probable cause to stop him. Accordingly, I
would affirm the district court’s denial of his motion to sup-
press and respectfully dissent from the majority’s decision.13




  12
     The majority asserts that my concern regarding North Carolina’s certi-
fication test is nothing more than a policy consideration. I express no pol-
icy view as to whether North Carolina, Ohio, or any other state should
certify officers in this manner, or what their legislatures should require in
the way of traffic stops and convictions. My concern is that the majority
has invalidated what appears to be a well-accepted test for police officers
to demonstrate their proficiency in this area, without any evidentiary sup-
port and based instead upon their common sense and judicial notice of the
mathematical formula for speed. If the reliability of North Carolina’s certi-
fication procedure is to be challenged, I believe we should leave it to a
defendant who chooses to challenge it and who introduces evidence in
support of that challenge, and that the government should be given the
opportunity to defend it.
   13
      I would also affirm the district court’s decision that Deputy Elliott had
reasonable suspicion sufficient to prolong the stop and perform a canine
sniff while waiting for the BLOC information, and that he had probable
cause to conduct a search of the vehicle once the canine alerted to illegal
drugs.
