United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued September 12, 2014           Decided December 19, 2014

                         No. 13-7077

                   DARLENE C. ROBINSON,
                       APPELLANT

                               v.

 WASHINGTON METROPOLITAN AREA TRANSIT AUTHORITY,
                   APPELLEE


         Appeal from the United States District Court
                 for the District of Columbia
                     (No. 1:11-cv-00723)


    Charles C. Parsons argued the cause and filed the briefs for
appellant.

    Kathleen A. Carey argued the cause and filed the briefs for
appellees. Mark F. Sullivan entered an appearance.

    Before: GARLAND, Chief Judge, SRINIVASAN, Circuit
Judge, and SENTELLE, Senior Circuit Judge.

    Opinion for the Court filed by Chief Judge GARLAND.
                                  2

      GARLAND, Chief Judge: A bus driver, one Mr. Bumpass,
hits the brakes as he approaches a stop sign. The plaintiff, a
passenger on the bus, falls backward and breaks her leg. The
question on appeal is whether, in light of the evidence presented
at trial, a reasonable jury could find the bus company liable for
the plaintiff’s injury. Applying the common law of the District
of Columbia, we affirm the district court’s conclusion that a
reasonable jury could not.

                                  I

      On the morning of April 16, 2008, Darlene Robinson
boarded a Washington Metropolitan Area Transit Authority
(WMATA) bus at the Gallatin and 11th Street stop in Northeast
Washington, D.C. She paid her fare and proceeded past bus
driver Ronald Bumpass. Robinson continued down the aisle,
gripping the seat-back handrails as she went. Bumpass closed
the doors and began driving away from the stop. Shortly
thereafter, Bumpass hit the brakes as he approached a stop sign
on Gallatin Street. As the bus decelerated, Robinson -- who was
still standing, facing the back of the bus -- lost her grip on a
handrail, fell in a twisting motion, “landed on [her] . . .
backside,” and broke her left leg. J.A. 514 (Robinson
Testimony).

    Robinson sued WMATA, alleging that Bumpass’ negligent
operation of the bus caused her injury and that WMATA was
responsible.1 At trial, Robinson sought to prove Bumpass’
negligence on two theories. First, she sought to show that he


     1
     Robinson’s complaint named WMATA and “Bus Driver John
Doe” as defendants. J.A. 37. Although Robinson reserved the right
to amend her complaint when she learned the driver’s identity, she did
not do so. The parties have proceeded on the understanding that
WMATA is the sole defendant, and so do we.
                                3

violated WMATA’s standard operating procedures (SOPs).
Second, she sought to show that the “jerk” caused by Bumpass’
application of the brakes was of such extraordinary force that
his negligence could be inferred.

     In support of her claim that Bumpass was negligent because
he violated WMATA’s SOPs, Robinson presented the expert
testimony of Dr. Carl Berkowitz, a public transportation safety
engineer. Dr. Berkowitz testified that the National Academy of
Sciences and the U.S. Department of Transportation fund
research studies to address transportation safety issues, and that
the results and recommendations from those studies “emanate[]”
and “filter[] down” to “all the major transit agencies.” J.A. 270-
71. According to Berkowitz, those results and recommendations
have led to nationally agreed-upon safety standards that all
major cities in the United States, including the District of
Columbia, have implemented.

     Dr. Berkowitz then identified two WMATA SOPs relevant
to this case, and stated that each reflected the national standard
of care for city bus travel. First, a WMATA bus driver is
required to check his or her rearview mirror before departing
from a stop to confirm that all passengers are “secure” and
“prepared for vehicle movement.” J.A. 938, 941. Second, a
WMATA bus driver is instructed to start the bus “gradually” and
stop the bus “smoothly.” J.A. 942-43.

     Counsel for WMATA asked Dr. Berkowitz where and when
these national standards for safe bus travel were articulated.
Berkowitz replied that they were “developed from research,
which actually dates back to Hammurabi -- the Hammurabi
Code -- I guess [that] would be 3,500 years ago.” J.A. 458. He
also said that the “first major research in this area[] was in the
book of Deuteronomy.” Id.
                                4

     To establish that Bumpass violated the SOPs identified by
Dr. Berkowitz, Robinson called Bumpass himself to the stand.
Bumpass admitted that he did not check his mirror before
leaving the stop that morning. He knew there were several open
seats up front, he said, and he assumed Robinson had sat down
by the time he closed the doors and started driving. J.A. 667-68.

     In support of her alternative theory -- that Bumpass’
negligence was shown by the fact that his braking had caused
the bus to jerk with extraordinary force -- Robinson took the
stand to testify that the bus was going “fast, faster than normal
buses,” J.A. 513, and that it “was jerking and then [there] was an
abrupt stop,” J.A. 528. The abrupt stop, she testified, caused her
to lose her grip on the handrail and fall. J.A. 528-29.

     Robinson also presented the expert testimony of Dr. Jamie
Williams, a biomedical engineer, to explain how the force of the
bus’ movements caused her to lose her grip on the handrail and
fall down. Dr. Williams testified that a torsional force on
Robinson’s left lower leg, brought about by the deceleration of
the bus, caused her leg to break. Williams estimated that, based
on the maximum grip strength of a woman of similar age and
weight as Robinson, the “deceleration that would have
destabilized her” would have been roughly “.38 times gravity.”
J.A. 207. When asked on cross-examination if she had any
information relating to the actual strength of Robinson’s grip
that day, Dr. Williams acknowledged that she did not. She
testified that her conclusions were premised on the assumption
that Robinson had been holding onto the handrail as tightly as
she possibly could. J.A. 227-28.

     At the close of Robinson’s case and again at the conclusion
of all of the evidence, WMATA moved for judgment as a matter
of law under Federal Rule of Civil Procedure 50(a). The district
court reserved ruling on those motions and submitted the case to
                                5

the jury, which returned a verdict for Robinson and awarded her
$404,713.28 in damages. Thereafter, the court granted
WMATA’s renewed motion for judgment as a matter of law
under Rule 50(b). Robinson v. WMATA, 941 F. Supp. 2d. 61
(D.D.C. 2013).

     In granting judgment as a matter of law in favor of
WMATA, the court rejected Robinson’s effort to prove
negligence through the violation of WMATA’s standard
operating procedures. The court concluded that Dr. Berkowitz
had failed to show that either of the two SOPs reflected national
standards of care; that there was no evidence of “a causal
connection between the driver’s failure to check the internal
center mirror and [Robinson’s] injury,” id. at 69 n.5; and that the
“start gradually and stop smoothly” SOP could not serve as a
negligence standard because to treat it as such “would be
inconsistent with District of Columbia law,” id. at 71. The court
also rejected Robinson’s theory that Bumpass’ negligence could
be inferred from the bus’ jerk, concluding that the evidence was
insufficient to show that the jerk was of an extraordinary nature.

    Robinson filed a timely appeal, and that appeal is now
before us.

                                II

      We must affirm a Rule 50(b) judgment as a matter of law
“if, after viewing the evidence in the light most favorable to the
non-moving party and drawing all reasonable inferences, it is
clear that a reasonable jury could only have found for the
moving party.” Johnson v. WMATA, No. 90-7027, 1991 WL
214174, at *2 (D.C. Cir. 1991); see Conseil Alain Aboudaram,
S.A. v. de Groote, 460 F.3d 46, 50 (D.C. Cir. 2006). Federal
jurisdiction over this lawsuit arises under the WMATA
                                    6

Compact. See D.C. Code § 9-1107.01(81).2 The Compact
provides that WMATA shall be liable for the torts of its
employees “in accordance with the law of the applicable
signatory,” id. § 9-1107.01(80), which in this case is the District
of Columbia.3 The tort law of the District of Columbia therefore
controls our disposition, Briggs v. WMATA, 481 F.3d 839, 843
(D.C. Cir. 2007), and we must aim “to achieve the same
outcome [that] would result if the District of Columbia Court of
Appeals considered this case,” id. (quoting Novak v. Capital
Mgmt. & Dev. Corp., 452 F.3d 902, 907 (D.C. Cir. 2006)).

     In Johnson v. WMATA, we suggested that there are (at least)
two theories under which a plaintiff may recover in a bus
negligence case against WMATA. 1991 WL 214174, at *1.
First, a plaintiff may present direct evidence of negligence. For
example, evidence that a bus driver let himself be distracted
while driving can be sufficient to recover. See Sibert-Dean v.
WMATA, 721 F.3d 699, 701 (D.C. Cir. 2013) (affirming a
finding of negligence where the driver turned to look at teenage
girls). Evidence that a driver violated an applicable standard of
care can likewise be sufficient. See WMATA v. O’Neill, 633
A.2d 834, 841 (D.C. 1993). Second, a plaintiff may offer
circumstantial evidence of negligence by showing that the driver
caused a jerk “so violent or extraordinary that it could not have
been consistent with safe operation of the bus.” Johnson, 1991

     2
      The Compact -- an interstate agreement among the District of
Columbia, Maryland, and Virginia -- created WMATA. See Pub. L.
No. 89-774, 80 Stat. 1324 (1966) (codified as amended at D.C. Code
§ 9-1107.01 et seq.). Section 81 of the Compact provides that federal
district courts shall have original jurisdiction, concurrent with the state
courts of the three signatories, “of all actions brought by or against”
WMATA. D.C. Code § 9-1107.01(81).
     3
     WMATA does not dispute that it is liable for Robinson’s injury
if Bumpass was negligent and if that negligence caused the injury.
                               7

WL 214174, at *2 (citing Boyko v. WMATA, 468 A.2d 582, 584
(D.C. 1983)).

     The question on this appeal is whether Robinson presented
sufficient evidence for a reasonable jury to find negligence
under either theory. We address the direct evidence theory in
Part III and the circumstantial evidence theory in Part IV.

                               III

     Under District of Columbia law, a plaintiff seeking to prove
her case through direct evidence of negligence has the burden of
establishing three elements: (1) “the applicable standard of
care”; (2) “a deviation from that standard by the defendant”; and
(3) “a causal relationship” between the deviation and the injury
she suffered. Varner v. District of Columbia, 891 A.2d 260, 265
(D.C. 2006). To prove her case on this theory, Robinson argued
that WMATA’s check-your-mirror and “start gradually, stop
smoothly” SOPs constituted applicable standards of care; that
Bumpass deviated from those standards; and that her injury was
the consequence of those deviations. On appeal, she challenges
the district court’s conclusion that she failed to establish that
either of the SOPs constituted an applicable standard of care
and, moreover, that she failed to show that the deviation from
the check-your-mirror SOP caused her injury. We address the
district court’s analysis of each SOP below.

                               A

     Under the check-your-mirror SOP, a WMATA bus driver
is expected to check his rearview mirror and “[m]ake sure all
passengers are secure before moving the bus.” J.A. 938.
According to Robinson’s expert, Dr. Berkowitz, “secure” means
                                  8

that the passengers “are holding on to something.” J.A. 442.4
The district court concluded both that Berkowitz’s testimony
was insufficient to show that this SOP constituted a national
standard of care in the public transportation industry, and that
Robinson failed to show that violation of the SOP caused her
injury.

     Ordinarily, the applicable standard of care is the traditional
reasonable person standard, which the “jury can
ascertain . . . without the aid of expert testimony.” Godfrey v.
Iverson, 559 F.3d 569, 572 (D.C. Cir. 2009). But where “the
subject in question is so distinctly related to some science,
profession or occupation as to be beyond the ken of the average
layperson,” the plaintiff must proffer expert testimony to
establish the applicable standard of care. Id. (internal quotation
marks omitted); accord Varner, 891 A.2d at 265. Put
differently, an expert is necessary unless the subject matter is
“within the realm of common knowledge and everyday
experience” of average jurors. Godfrey, 559 F.3d at 572
(internal quotation marks omitted).

     When an expert witness is required, the expert must “clearly
articulate and reference a standard of care by which the
defendant’s actions can be measured.” Varner, 891 A.2d at 269
(internal quotation marks and emphasis omitted). Especially in
cases involving safety standards, the expert must also show that


     4
      Dr. Berkowitz had initially tried to testify that the national
standard of care required passengers to be seated before a bus driver
started driving. But the district court barred that testimony on the
ground that WMATA has an express policy permitting passengers to
stand while riding a bus, and that this policy constitutes a
“discretionary decision” that is “shielded from suit” under § 80 of the
WMATA Compact. Robinson v. WMATA, 858 F. Supp. 2d 33, 37
(D.D.C. 2012). Robinson does not appeal that ruling.
                               9

the particular practice at issue reflects a national standard of
care. See, e.g., Novak v. Capital Mgmt. & Dev. Corp., 570 F.3d
305, 313 (D.C. Cir. 2009); Briggs, 481 F.3d at 846-47; Clark v.
District of Columbia, 708 A.2d 632, 635 (D.C. 1997). An
expert’s personal opinions or “unsupported assertion[s] as to the
national standard of care” are insufficient. Clark, 708 A.2d at
635. Further, although internal agency manuals such as
WMATA’s standard operating procedures may provide evidence
bearing on the standard of care, they do not, on their own,
establish the national standard. Briggs, 481 F.3d at 848; Varner,
891 A.2d at 269. Rather, the expert must show that the practices
to which the agency has committed reflect “the national standard
of care and not a higher, more demanding one.” Clark, 708
A.2d at 636.

     Robinson argues, first, that the district court improperly
required her to establish the standard of care via an expert
witness. Indeed, we seriously doubt that determining whether
it is reasonable to start a motor vehicle without checking to
make sure one’s passengers are secure is outside “the realm of
common knowledge and everyday experience” of average
jurors. Godfrey, 559 F.3d at 572; see, e.g., O’Neill, 633 A.2d at
841 & n.14 (holding that an expert was not required to establish
that a WMATA bus driver should have alerted the police when
two drunk men loudly threatened and later assaulted another
passenger aboard a Metrobus); WMATA v. Young, 731 A.2d 389,
396 (D.C. 1999) (holding that whether a bicyclist “was able to
avoid colliding with” a city bus is not “beyond the ken of the
average layperson”) (internal quotation marks omitted); cf. BOB
DYLAN, Subterranean Homesick Blues, on BRINGING IT ALL
BACK HOME (Columbia Records 1965) (“You don’t need a
weatherman to know which way the wind blows.”).

     The problem is that Robinson forfeited this argument. The
district court’s first opinion in this case, denying WMATA’s
                                10

motion for summary judgment, indicated that an expert was
required to establish the standard of care because the subject was
“beyond the ken of the average layperson.” Robinson v.
WMATA, 858 F. Supp. 2d 33, 39 (D.D.C. 2012) (internal
quotation marks omitted). Robinson did not demur. When
WMATA moved for judgment as a matter of law at the close of
Robinson’s case,5 the court again opined that “there has to be
expert testimony about the national standard of care,” J.A. 603-
04, and Robinson did not disagree. In accordance with its
expressed view, the court then instructed the jury that, “You can
only determine the standard of care required of WMATA from
the testimony of the expert witnesses regarding that standard.”
Jury Instructions 36, § 9.08. Again, Robinson did not object.
Finally, when WMATA filed a renewed motion for judgment as
a matter of law after the verdict, maintaining that an expert was
required because the question was “beyond the ken of the
average layperson,” J.A. 796, Robinson did not object on that
ground.

     A “fundamental principle of appellate review generally bars
a party who failed to preserve an argument in a lower tribunal
from raising it on appeal absent plain error or exceptional
circumstances.” Bahlul v. United States, 767 F.3d 1, 9 (D.C.
Cir. 2014) (en banc); see Salazar ex rel. Salazar v. District of
Columbia, 602 F.3d 431, 434 (D.C. Cir. 2010). We detect no
exceptional circumstances here. And because District of
Columbia courts have required expert testimony in many cases
that, “on first blush, appear to be within the realm of common
knowledge,” Briggs, 481 F.3d at 845, we cannot find that it was
plain error to require expert testimony to establish the standard
of care in this case. See id. (citing decisions requiring experts in
cases involving the maintenance of leaning trees, the tightness


    5
     WMATA renewed that motion, by incorporation, at the
conclusion of all of the evidence.
                               11

of handcuffs, the maintenance of street lights, and the choice
between a crosswalk and a stop sign); Burke, 685 F.3d at 1106
n.2 (same).

     Robinson argues, second, that her expert’s testimony was in
any event sufficient to establish that WMATA’s check-your-
mirror SOP reflected a national standard. We admit to being
tempted to delve more deeply into the question of whether this
SOP really “developed from research, which actually dates back
to Hammurabi” and “the book of Deuteronomy.” J.A. 458.6 But
we need not resolve that question either. Whether or not Dr.
Berkowitz successfully showed that the check-your-mirror SOP
reflected a national standard, this negligence theory suffers from
an independent ailment: lack of causation.

     As the district court correctly found, “Robinson did not
introduce any evidence supporting a causal connection between
the driver’s failure to check the internal center mirror and her
injury.” Robinson, 941 F. Supp. 2d. at 69 n.5. If Bumpass had
looked in the mirror, what would he have seen? According to
Robinson’s testimony, he would have seen that she was holding
onto a handrail, J.A. 512 -- exactly what Dr. Berkowitz testified
the standard of care required him to confirm before moving the
bus, see J.A. 442. Accordingly, had Bumpass followed the SOP,
he would have done just what he did do -- move the bus -- and
hence any deviation from the standard could not have caused
Robinson’s injury.

     At oral argument, Robinson’s counsel attempted to remedy
this fatal shortcoming by asserting that Robinson was not


    6
     Cf. CODE OF HAMMURABI § 197 (L.W. King. trans. 1915) (c.
1780 B.C.), available at http://www.fordham.edu/halsall/ancient/
hamcode.asp (“If he break another man’s bone, his bone shall be
broken.”).
                                   12

actually secure because she was only holding onto a seat-back
handrail, as opposed to one of the bus’ vertical poles. Oral Arg.
Recording at 16:49-17:26. But Dr. Berkowitz never testified
that a passenger would not be considered “secure” unless she
were holding on to a vertical pole (as opposed to a handrail). To
the contrary, his testimony indicated that a passenger holding
onto a handrail would be considered secure. J.A. 442 (stating
that “we want to make sure that [passengers] are holding on to
something”) (emphasis added). Therefore, Robinson failed to
establish “a causal relationship between [Bumpass’] deviation
and [her] injury.” Varner, 891 A.2d at 265.7

                                   B

     Robinson’s effort to prove negligence by establishing a
violation of the “start gradually, stop smoothly” SOP fares no
better.

     First, Robinson’s argument that an expert was not required
to establish this SOP as the standard of care fails for the same
reason we identified above: She did not object to the jury
instruction that required expert testimony to show that a
WMATA operating procedure evidenced a national standard of



     7
      There is a second causation problem as well. The SOP in
question says that a driver should check the mirror before moving the
bus; it says nothing about checking before stopping the bus. But
Robinson did not fall when the bus first began moving; she fell only
as it came to a stop. Robinson argues that Bumpass’ start and
subsequent stop were “packed into just seven seconds,” Robinson Br.
29, suggesting that his failure to look in the mirror at the start had an
effect that continued through the stop. In light of the causation
problem identified in the text, we need not consider whether this
argument is sufficient to bridge the gap between the start and the stop.
                               13

care. And as we said, that instruction did not constitute plain
error.

     Second, as the district court found, WMATA cannot be
liable for violations of the “start gradually and stop smoothly”
SOP because that “would be inconsistent with District of
Columbia law.” Robinson, 941 F. Supp. 2d. at 71. As we
discuss in Part IV, WMATA is not liable under District law for
the normal jerks and jolts commonly associated with bus travel.
Johnson, 1991 WL 214174, at *2; Fells, 357 A.2d at 395; see
Connor v. Wash. Ry. & Elec. Co., 43 App. D.C. 329, 333-34
(D.C. 1915). Much more is required than merely failing to start
gradually or stop smoothly. Rather, the common law of the
District requires evidence that a jerk was of “extraordinary”
force before an abrupt stop may be taken as proof of negligence.
See Johnson, 1991 WL 214174, at *2; Fells v. WMATA, 357
A.2d 395, 395 (D.C. 1976). Accordingly, whether or not the
“start gradually, stop smoothly” SOP reflects a nationally
accepted practice, it cannot be the standard of care for purposes
of a negligence action governed by District of Columbia tort
law. Robinson cannot recover against WMATA merely by
showing that Bumpass did not achieve a gradual start or a
smooth stop.

                               IV

     What remains is Robinson’s alternative argument that she
provided circumstantial evidence of negligence by showing that
the bus driver caused a jerk “so violent or extraordinary that it
could not have been consistent with safe operation of the bus.”
Johnson, 1991 WL 214174, at *2 (citing Boyko, 468 A.2d at
584; Fells, 357 A.2d at 395-96). A plaintiff may pursue
damages under this theory of liability without introducing expert
testimony regarding the standard of care. See, e.g., Brighthaupt
                               14

v. WMATA, No. 97-7217, 1998 WL 794814, at *1 (D.C. Cir.
1998).

     As we have just noted, WMATA is not liable for the normal
“jerks or jars” that occur during city bus rides. Fells, 357 A.2d
at 395 (quoting D.C. Transit System, Inc. v. Perry, 337 A.2d
224, 225 (D.C. 1975)). “Because ‘jerks’ occur often in the
normal operation of a bus, evidence of a jerk that resulted in
injury is not usually enough for a jury to infer negligence. If it
were, WMATA could be held liable for many common
accidents that are no fault of the driver.” Johnson, 1991 WL
214174, at *2. Instead, a plaintiff may “recover against the bus
company only by showing ‘that the “jerk” or “sudden start” was
of such unusual and extraordinary force that it could not
reasonably be said to have happened in the ordinary operation
of the vehicle.’” Boyko, 468 A.2d at 583-84 (quoting Wiggins
v. Capital Transit Co., 122 A.2d 117, 118 (D.C. 1956)); see
Brighthaupt, 1998 WL 794814, at *1.

     Such “‘unusual and extraordinary force,’” the District of
Columbia Court of Appeals has said, “cannot be inferred from
‘mere descriptive adjectives and conclusions’ alone.” Boyko,
468 A.2d at 584 (quoting Wiggins, 122 A.2d at 118). Rather,
reviewing courts must focus on “the substance of the testimony,
not on its grammatical form.” Id. The critical question “is
whether the testimony, in whatever form it is offered, describes
movement that is ‘consistent with proper operation of the bus.’”
Id. (quoting WMATA v. Jones, 443 A.2d 45, 50 (D.C. 1982) (en
banc)).

     In Boyko, for example, the plaintiff testified that the bus’
jerk was “‘abrupt,’” “‘violent,’” and “unlike what she had come
to expect in her fifty years of riding buses.” 468 A.2d at 584-85.
Her treating physician further testified that “her injury was one
that ‘takes a considerable amount of violence.’” Id. at 583.
                               15

Finally, the bus driver admitted that, “when she pulled away
from the stop, she knew that the floor was wet and that appellant
had not yet reached a seat.” Id. Taken together, this testimony
was sufficient to send the case to a jury. Id. at 585. In Johnson,
by contrast, a witness’ statement that a bus’ jerk “wasn’t
normal” was insufficient. 1991 WL 214174, at *2. Likewise
insufficient was the testimony of Johnson’s doctor, who “did not
testify that the injury could only have been caused by a violent
motion of the bus.” Id.

     In support of her claim that her bus experienced an
extraordinary and violent jerk, Robinson testified that the bus
was going “fast, faster than normal buses,” J.A. 513, and that it
“was jerking and then [there] was an abrupt stop,” J.A. 528.
When asked how fast the bus was moving, Robinson said: “I
was not facing the driver, so I wasn’t aware of the speed. But I
could see the trees at the park going by swiftly as I was
proceeding to a seat.” J.A. 513. The abrupt stop, she testified,
caused her to lose her grip on the handrail and fall. J.A. 528-29.

     As an initial matter, we reject WMATA’s contention that
Robinson’s testimony was insufficient merely because no other
witness corroborated it. It is true that plaintiffs who recover
under this theory often present testimony of non-party witnesses
who can in some manner corroborate the extreme nature of the
bus’ jerk. See, e.g., Boyko, 468 A.2d at 585; Brighthaupt, 1998
WL 794814, at *1. But the District of Columbia cases do not
hold that a plaintiff cannot recover on the basis of her testimony
alone. To the contrary, as the Boyko court observed, if
WMATA is arguing that there is “some fancied defect in . . . the
self-evident interest of a party in the outcome of the case, it is
unpersuasive.” 468 A.2d at 584.

   Nonetheless, we agree with the district court that
Robinson’s testimony “does not give rise to an inference that the
                                 16

deceleration was ‘of such unusual and extraordinary force that
it could not reasonably be said to have happened in the ordinary
operation of the vehicle.’” Robinson, 941 F. Supp. 2d at 73
(quoting Boyko, 468 A.2d at 584). The strongest part of her
testimony -- that the bus was traveling “fast, faster than normal
buses” -- is not enough to recover on this theory. See Boyko,
468 A.2d at 584 (distinguishing as insufficient such testimony
in Perry, 337 A.2d at 225, where the plaintiff described the bus’
movement as “unusually fast”). Robinson acknowledged that
she “wasn’t aware of the [bus’] speed,” J.A. 513, and she
provided no context for what she meant by “normal.” Traveling
faster than “normal” does not mean that the movement was
inconsistent with safe or proper operation, let alone that the stop
was. Nor was Robinson’s testimony -- that the bus’ movement
was “jerking” and the stop “abrupt” -- inconsistent with a
description of the jerks and jolts that commonly occur aboard
city buses. See Fells, 357 A.2d at 395. Under District law,
“‘testimony of a sudden stop and resulting injuries does not, by
itself, raise a permissible inference of negligence.’” Boyko, 468
A.2d at 584 (quoting Fells, 357 A.2d at 395-96); cf. Wiggins,
122 A.2d at 118 (noting that “statements that a street car ‘started
violently,’ ‘started with a violent jerk,’ . . . and the like, are not
of themselves sufficient to show negligent operation” (citation
omitted)).

     The testimony of Robinson’s biomedical expert, Dr.
Williams, does not rescue her case. Dr. Williams was not
Robinson’s treating physician and never talked to her. J.A. 243.
Williams did testify that, assuming Robinson was holding the
handrail with the maximum grip strength of a woman of similar
age and weight, the “deceleration that would have destabilized
her” would have been about “.38 times gravity.” J.A. 207. But
assuming that “.38 times gravity” constitutes an extraordinary or
violent force (no evidence was offered on the point), there was
no testimony that Robinson was capable of exerting the
                               17

maximum grip strength of a woman of her age and weight, and
no testimony that she was holding on as tightly as she could.
Indeed, Dr. Williams acknowledged that she had no information
at all regarding how tightly Robinson was actually holding the
handrail, and agreed that, if Robinson were “not holding onto
the hand hold with everything she’s got, it would take
less . . . deceleration to disrupt her grip.” J.A. 227-28. As a
consequence, Williams’ testimony left the jury unable to do
anything more than speculate about the actual force of the stop.
And “[s]ufficiency of the evidence to support a claim for relief
may not be established by jury speculation.” Milone v. WMATA,
91 F.3d 229, 232 (D.C. Cir. 1996).

     In sum, because Robinson’s testimony was “consistent with
proper operation of the bus,” and because a jury could only infer
from Dr. Williams’ testimony “that it was possible that Ms.
Robinson’s injury resulted from significant force,” Robinson,
941 F. Supp. 2d at 73-74 (internal quotation marks omitted), the
district court properly granted judgment as a matter of law in
favor of WMATA.

                                V

    For the foregoing reasons, we conclude that neither of the
two negligence theories proffered by the plaintiff was supported
by evidence sufficient to sustain a jury verdict in her favor. The
judgment of the district court is therefore

                                                        Affirmed.
