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January 14, 2000

Record No. 990181






Present: All the Justices

J. Michael Gamble, Judge

In this appeal from a judgment for the
defendant in a negligence action, we determine whether the trial
court abused its discretion in admitting the testimony of an
automobile accident reconstruction expert concerning
"average" human perception and reaction times.

In June 1997, April A. Keesee filed a motion
for judgment against Howard Alexander Donigan alleging that
Donigan negligently operated his motor vehicle, which collided
with the vehicle she was driving and caused her to sustain
personal injuries. Keesee alleged, among other things, that
Donigan failed to keep a proper lookout while driving and failed
to keep his vehicle under proper control.

The following evidence was presented in a jury
trial. On September 8, 1996, at about 3:15 a.m., Keesee was
injured when the car she was driving on State Route 655 in
Amherst County collided with Donigan’s vehicle. The accident
occurred on the two-lane roadway as Donigan approached Keesee’s
vehicle from the opposite direction.

A large fallen tree limb blocked Donigan’s lane
of travel from the shoulder of the road to a point near the
center line mark. When Donigan saw the tree limb, he was able to
steer his vehicle so that the tires on the driver’s side passed
through the small clearing between the end of the limb and the
center line mark of the road. The front tire on the passenger’s
side rolled over the tree limb, but the rear tire on that side
hit the limb and the vehicle was "thrown" into the path
of Keesee’s oncoming vehicle. The front left corners of the two
vehicles collided.

Donigan testified that he was travelling at a
maximum speed of 35 miles per hour when he saw the limb blocking
his lane of travel. He stated that the headlights on his vehicle
illuminated the roadway ahead for a distance of about 75 to 100

Michael Gould, a friend of Keesee’s, testified
that he was driving his vehicle on Route 655 in the same
direction as Keesee about 50 yards ahead of Keesee’s car. When
Gould saw the tree limb blocking the lane in which Donigan’s
vehicle was approaching, Gould "flashed" his vehicle’s
high beam headlights several times to warn Donigan of the
approaching danger. Donigan testified that he thought Gould was
trying to inform him that Donigan had his own high beam
headlights activated.

Over Keesee’s objection, the trial court
permitted Donigan to present the testimony of Stephen B.
Chewning, who qualified as an expert in accident reconstruction,
concerning "average" human perception and reaction
times. Before ruling on Keesee’s objection, the trial court
permitted counsel to question Chewning outside the jury’s
presence. During this questioning, Chewning agreed that many
factors, including a person’s physical condition, visual acuity,
and cognitive abilities, affect the length of time required for
that person to perceive and react to an unexpected highway
danger. Chewning stated that an older person would have slower
than "average" reaction times, while an athlete or an
airplane pilot would react to sudden events faster than
"average." Chewning acknowledged that he had not tested
Donigan’s vision or assessed his cognitive and physical abilities
but assumed that they were "normal." The trial court
overruled Keesee’s objection to Chewning’s testimony.

Chewning testified before the jury regarding a
person’s perception of and reaction to an unexpected hazard while
driving. He testified that based on numerous industry studies
conducted by universities and government agencies over the past
sixty years, a driver requires three-quarters of a second,
"on average," to perceive a hazard. That driver also
takes another three-quarters of a second to react to what he has
perceived. Thus, Chewning concluded that a driver requires an
average of 1.5 seconds between the time he first recognizes a
hazard and the time he executes an action to avoid the hazard.
Chewning stated that this figure is subject to a variation of as
much as four-tenths of a second, depending on the individual

Chewning explained that this
"average" period of 1.5 seconds is an "industry
standard" that has remained constant since the 1930’s, and
generally is used in accident reconstruction unless there is a
specific reason not to use it. He also testified, based on
mathematical calculations, that a vehicle traveling 35 miles per
hour covers 51.3 feet per second.

In his closing argument, Donigan’s counsel used
Chewning’s testimony to support his argument that since Donigan
required 1.5 seconds to perceive and react to the presence of the
tree limb, he did not have sufficient time to avoid the accident.
The jury returned a verdict in favor of Donigan, and the trial
court entered judgment in accordance with the jury verdict.

On appeal, Keesee argues that the trial court
erred in admitting Chewning’s testimony concerning
"average" perception and reaction times. She contends,
among other things, that Chewning’s testimony concerning this
test data was inadmissible because it failed to consider whether
Donigan’s physical and mental condition may have affected his
perception and reaction times.

In response, Donigan contends that the
challenged testimony was properly admitted because it assisted
the trier of fact in understanding the process by which a person
perceives and reacts to an unexpected hazard while driving. He
asserts that Chewning did not express an opinion concerning
Donigan’s specific reaction and perception times during the
accident, but simply "educated the jury" regarding a
technical aspect of the case. Donigan argues that Chewning’s
testimony provided the jury with the knowledge necessary to
consider Donigan’s perception and reaction in determining whether
he acted as a reasonable person would have acted under the
circumstances presented. We disagree with Donigan’s arguments.

The standard of review that we apply is well
established. The admission of expert testimony is a matter within
the sound discretion of the trial court, and we will reverse the
trial court’s judgment only when the court has abused this
discretion. Tarmac Mid-Atlantic, Inc. v. Smiley Block Co.,
250 Va. 161, 166, 458 S.E.2d 462, 465 (1995); Brown v. Corbin,
244 Va. 528, 531, 423 S.E.2d 176, 178 (1992).

We first note that Keesee did not raise a
hearsay objection to the admission of the disputed testimony or
argue that the testimony failed to qualify for admission under
the provisions of Code ? 8.01-401.1. See, e.g., Todd
v. Williams
, 242 Va. 178, 182-83, 409 S.E.2d 450, 452-53
(1991). Therefore, we consider Keesee’s argument apart from these
legal principles.

Expert testimony generally is admissible in
civil cases if it will aid the trier of fact in understanding the
evidence. See Code ?? 8.01-401.1 and –401.3; Tittsworth
v. Robinson
, 252 Va. 151, 154, 475 S.E.2d 261, 263 (1996).
However, the admission of expert testimony is subject to certain
fundamental requirements, including the requirement that the
evidence be based on an adequate foundation. Id.; Tarmac
Mid-Atlantic, Inc.
, 250 Va. at 166, 458 S.E.2d at 465-66; Lawson
v. Doe
, 239 Va. 477, 482-83, 391 S.E.2d 333, 336 (1990).
Thus, expert testimony is inadmissible if it is founded on
assumptions that have an insufficient factual basis. Tittsworth,
252 Va. at 154, 475 S.E.2d at 263; Tarmac Mid-Atlantic, Inc.,
250 Va. at 166, 458 S.E.2d at 466; see Gilbert v.
, 240 Va. 155, 160, 393 S.E.2d 213, 215 (1990).

In addition to these basic principles, we also
consider two recent decisions in which we have addressed the
admissibility of expert testimony offered to assist a trier of
fact in understanding general scientific or technical principles.
In Holmes v. Doe, 257 Va. 573, 578, 515 S.E.2d 117, 120
(1999), we held that the trial court did not abuse its discretion
in permitting an expert witness to explain the general
relationship between a vehicle "hydroplaning" and the
factors of wet road conditions, tire tread depth, and vehicular
speed. In Breeden v. Roberts, 258 Va. 411, 414-16, 518
S.E.2d 834, 836-37 (1999), we held that the trial court abused
its discretion in excluding expert testimony from a mechanic
regarding the effect that a frozen brake adjuster has on the
operation and performance of a vehicle.

In these two cases, the expert testimony
concerning those general scientific and technical principles did
not require any specific information about the drivers involved
in the cases, the condition of their vehicles, or other
circumstances in which the accidents occurred. Thus, the expert
testimony concerning general principles in these cases was
appropriate to aid the triers of fact in drawing their own
conclusions from the factual evidence received from the other
witnesses. See Holmes, 257 Va. at 578, 515 S.E.2d
at 120.

The expert testimony at issue in the present
case presents a distinct contrast from the type of expert
testimony approved in Breeden and Holmes. In those
cases, the experts did not attempt to relate the scientific
principles about which they testified to a particular driver or
vehicle. Here, however, Chewning applied his testimony to a
particular driver, Donigan, in the absence of foundation evidence
that would place him within the subject matter of Chewning’s
testimony concerning the "average" driver.

As stated above, Chewning acknowledged that the
"average" driver response times are subject to
variation, depending on a driver’s physical condition, visual
acuity, and cognitive abilities. However, he performed no tests
to establish that Donigan fell within the average range with
regard to such variables. When asked whether he performed tests
to determine Donigan’s perception time, Chewning replied,
"No, I’ve put him into an average category." When
questioned whether he merely assumed that Donigan’s reaction
times are "the standard," Chewning stated,

This testimony was insufficient to lay a
foundation for admission of the challenged evidence because the
probative value of that evidence rested on assumptions about
Donigan that had no factual basis in the record. See Tittsworth,
252 Va. at 154, 475 S.E.2d at 263; Tarmac Mid-Atlantic, Inc.,
250 Va. at 166, 458 S.E.2d at 466. Thus, we conclude that the
trial court abused its discretion in allowing Chewnings
testimony, absent foundation evidence that Donigan’s physical and
mental characteristics relevant to his perception and reaction
times placed him within the average range
of persons tested.

Contrary to Donigan’s assertion, this error was
not harmless. Chewning was the only expert witness who testified
on this subject, Donigan’s counsel emphasized this evidence in
his closing argument and, thus, the testimony may well have made
a lasting impression on the jury to Keesee’s prejudice. See
CSX Transp., Inc. v. Casale, 250 Va. 359, 367, 463 S.E.2d
445, 450 (1995).

For these reasons, we will reverse the trial
court’s judgment and remand the case for a new trial consistent
with the principles expressed in this opinion.

Reversed and remanded.