Accident Reconstruction Expert Witness’ Testimony About the Driver’s Speed at the Time of the Collision Admitted
Posted on January 28, 2025 by Expert Witness Profiler
This lawsuit stems from a motor vehicle accident. The two-vehicle collision occurred around 12:12 P.M. on January 4, 2023 in the left northbound lane of U.S. Highway 45, a divided four lane highway.
On the date and time in question, Plaintiff Kimberly Allcorn was driving a 2019 Kia Forte in the right lane of northbound traffic. She had been in Tupelo, Mississippi to pick up her car from a repair shop, and she intended to return to her residence in Corinth, Mississippi. Defendant Pamela Kay Beach was operating a 2023 Kenworth tractor-trailer truck that was owned by Western Express. Allcorn was traveling ahead of Beach on the roadway, both heading in the same direction.
After her vehicle began to exhibit additional problems, Allcorn decided to return to Tupelo. She switched from the right to the left lane of northbound traffic in an effort to proceed into a turn lane so that she could turn around and drive south back to Tupelo. Prior to the collision, Beach was traveling in the left lane at a higher rate of speed than Allcorn. When Allcorn switched into the left lane, Beach applied her brakes but a collision between the vehicles nonetheless occurred with the front of Beach’s tractor impacting the back of Allcorn’s car.
The posted speed limit in the area was 65 mph. The dash cam footage indicated that Beach was traveling 71 mph before she applied her brakes.
Allcorn filed suit against Beach and Western Express. She brought claims for negligence and negligence per se. On June 10, 2024, Allcorn designated Soan Chau as her expert in accident reconstruction. Chau prepared two reports summarizing his conclusions about the case. Defendants contended that the Court should prevent Chau from testifying because his opinions fell below the requisite threshold for expert testimony.
Accident Reconstruction Expert Witness
Soan Chau is a transportation consultant specializing in vehicular accidents with over twenty years of experience in analyzing cases involving passenger cars, tractor-trailers, motorcyclists, bicyclists, and pedestrians. He has analyzed over a thousand cases and has been intimately involved in scene preservation and documentation, surveying, reconstruction, simulation, animation, human factors and other transportation related matters.
Chau is also a certified Event Data Recorder (commonly known as “black box”) analyst and retriever, for both commercial vehicles and passenger cars.
Discussion by the Court
Chau’s Expert Testimony
In his initial report dated June 7, 2024, Chau opined that based on his calculations involving time, speed, and distance, Beach could have avoided the collision if she had been traveling 65 mph when Allcorn initiated her lane change from the right lane to the left lane.
On July 8, 2024, the Defendants’ accident reconstruction expert witness, Benjamin Smith, prepared his written report. Smith identified errors in Chau’s calculations—namely, Smith opined that the calculations contained in Chau’s report equated to Beach’s speed being 76 mph, which is demonstrably false based on the dash cam footage indicating that she was traveling 71 mph. Smith ultimately concluded that based on his own calculations, even if Beach had been traveling at the posted speed limit of 65 mph, she could not have avoided the collision.
After Smith pointed out the errors in Chau’s calculations, Chau prepared a supplemental report. In that report, Chau corrected the mathematical errors that Smith identified. After doing so, Chau again concluded that if Beach had been traveling at 65 mph instead of 71 mph, she could have avoided the collision.
In the supplemental report, Chau reached the following conclusions:
1. Based on the materials that are available at the time of this report, it is safe to conclude that, had the tractor trailer been traveling at the speed limit of 65 mph:
a. There would have been approximately 84 feet between the tractor trailer and the Kia, when the lead vehicle (Kia) arrive [sic] at the same collision point
b. At an 84 feet distance between the vehicles, the tractor-trailer driver would have more time to slow down, make lane change, release accelerator, or brake
c. Kimberly Allcorn would also have entered the left turn lane by the time the tractor trailer arrive [sic] at point of collision
2. Because the tractor trailer was over the speed limit the entire 10 seconds (1.1 second braking) leading up to the collision, the Kia was not able to clear the left travel lane
Defendant’s Arguments
The Defendants emphasized three distinct arguments that they contended constituted bases for the exclusion of Chau’s testimony:
(1) that his opinions were not relevant and did not assist the trier of fact;
(2) that his opinions had “no methodology or principles”; and
(3) that his prior opinions in another case contradicted his opinions here.
Analysis
Relevance
Defendants argued that “Chau’s opinion is that Beach would not have been at the accident scene at the same time as Plaintiff if Beach had not been traveling 70 to 71 miles per hour. Because such an opinion is not valid under Mississippi law, the opinion is irrelevant and must be excluded.” The Defendants contended that multiple Mississippi federal and state court cases supported their contention that Beach’s speed is irrelevant.
The Court found that the Defendants mischaracterized Chau’s conclusions. The Court noted that Chau did not offer any opinion about Beach’s speed earlier in the trip. Instead, he reached conclusions as to whether Beach traveling the speed limit at the time of the collision and the seconds leading up to the collision would have enabled her to avoid the collision.
The Court found it difficult to see how the driver’s speed at the time of the collision, along with a concomitant conclusion that a slower speed would have enabled the Defendant to avoid the accident, lacked significant relevance in a case of this nature. The argument that speed was entirely irrelevant missed the mark. The Court rejected the Defendants’ argument.
Methodology
Initial Report
In his initial report, Chau provided the following information in a section described as “Video Analysis”:
a. currently only 10 seconds of footage before the collision was available
b. 8 seconds after collision
c. Impact occurred at +1.00
d. The 18 second Video Footage does not have evenly spaced time
e. At T= -1.80 seconds, Kia encroached into the left travel lane; the tractor-trailer was traveling at 71 mph
f. At IMPACT T= +1.00, Kia was approximately from auxiliary lane for median break; tractor trailer V=57 mph
g. The total distance traveled by the tractor trailer during 11 seconds (of video footage) prior to collision is approximately 1237 feet
h. Travel distance at 65 mph for 11 seconds is 1049 feet
Based on that information, Chau concluded that, if the tractor trailer had been traveling at the speed of 65 mph, “there would have been approximately 188 feet between the tractor trailer and the Kia, when the lead vehicle (Kia) arrive [sic] at the same collision point.” He additionally concluded that Allcorn “would also have entered the left turn lane by the time the tractor trailer arrived at point of collision.”
Supplemental Report
As noted above, the Defendants’ expert witness, Benjamin Smith, prepared a report that identified errors in Chau’s calculations.
Chau then prepared a supplemental report. In that report, the “Video Analysis” section contains much of the same information listed above but sub-sections (d), (f), and (g) were slightly different and provided as follows:
d. The 18-second video footage appeared to be at approximately 10 Hertz
f. At IMPACT T= +1.00, Kia was approximately 50 feet from beginning of auxiliary lane for median break; tractor trailer V=57 mph
g. The total distance traveled by the tractor trailer during 11 seconds (of video footage) prior to collision is approximately 1133 feet
The supplemental report then goes on to provide the following additional information:
11. Had the tractor trailer was traveling [sic] 65 mph for 11 seconds, there would be approximately 84 feet between the tractor trailer and the Kia Forte when Allcorn arrives that [sic] the same collision point (POC)
12. As seen in the video, this tractor trailer can decelerate from 70-57=13 mph in 1.1 second [sic], traveling a distance of approximately 102 feet
13. At 65mph [sic], the same decelerate [sic] from 65-52=13 mph in 1.1 second [sic], tractor trailer would travel a shorter distance of 94 feet
16. At collision, the Kia Forte’s front bumper appears to be within 20 to 30 feet of the beginning of the auxiliary lane
17. There was approximately 40 to 50 percent overlap between the tractor trailer and the Forte at impact
19. For every incremental seconds [sic] Beach was traveling at 65 mph beyond the 10 seconds (before braking), the incremental increase in distance would be (71-65)1.47=8.8 feet.
He ultimately reaches the same conclusion—that Allcorn would have been able to reach the left turn lane before the collision if Beach had been traveling at 65 mph prior to the collision..
Defendant’s Argument
The Defendants poked numerous holes in Chau’s conclusions. For instance, they noted that he provided no explanation for the change in his calculations from the initial report to the supplemental report. They also emphasized that in the initial report, Chau did not include a specific distance that Allcorn’s vehicle was from the turn lane at the time of the collision but that in page 3 of his supplemental report, he indicated a distance of 50 feet and then later referenced a distance of 20-30 feet. The Defendants ultimately contended that Chau was “simply putting numbers in his report to make it seem scientific.”
While the Court was cognizant of the Defendants’ concerns, it was noted that they concerned the weight of Chau’s testimony, not its admissibility. In his report, Chau included the formula that he used to reach his ultimate conclusion that Allcorn would have been able to reach the left turn lane ahead of Beach (and avoid the collision) if Beach had been traveling at a speed of 65 mph. The Defendants may disagree with those calculations, believe that they contain errors, and/or that they do not take into account all relevant information—the Court held that they will certainly be given an opportunity to cross-examine Chau on those topics at trial.
But to altogether exclude Chau at this stage of the proceedings would go too far, in this Court’s view. The Defendants have not shown that Chau failed to engage in reliable methodology in reaching his conclusions—just that they disagree with those conclusions.
Prior Testimony
Lastly, the Defendants pointed to testimony that Chau provided in a previous case and contended that his testimony here is contradictory to his conclusion in that case. This Court is concerned, however, with the methodology that Chau has employed in this case and whether his methodology is sufficiently relevant and reliable to be admitted into evidence. In other words, the Defendants will be given latitude to cross-examine Chau about his prior testimony; however, this is again an insufficient basis to completely exclude his testimony.
Held
The Court denied the Defendants’ motion to exclude the testimony of Plaintiff’s accident reconstruction expert witness, Soan Chau.
Key Takeaway:
The Court concluded that Chau’s testimony was admissible, primarily because his methodology met the basic threshold for admissibility, even though there were some inconsistencies in his calculations. The Court emphasized three key points in its reasoning:
- Relevance: The Court rejected the Defendants’ argument that speed was irrelevant, noting that Chau’s analysis of how the speed limit would have affected the collision outcome was highly relevant to the case.
- Methodology: While acknowledging the Defendants’ concerns about calculation changes and inconsistencies in Chau’s reports, the Court determined these were issues of weight rather than admissibility. The Court noted that Chau had included his formula and analytical process in his reports, providing a sufficient methodological foundation.
- Prior Testimony: The Court found that potential contradictions between Chau’s current testimony and his testimony in a previous case were matters for cross-examination rather than grounds for exclusion.
Please refer to the blog previously published about this case:
2. Accident Reconstruction Expert Witness’ Supplemental Report Correcting Mathematical Errors Admitted
Case Details:
| Case caption: | Allcorn v. Beach |
| Docket Number: | 1:23cv121 |
| Court: | United States District Court for the Northern District of Mississippi, Aberdeen Division |
| Dated: | January 23, 2025 |
