XIV. Principles of Accident Reconstruction in Commercial Vehicle Cases

Below is the fourteenth chapter, “Principles of Accident Reconstruction in Commercial Vehicle Cases,” of Understanding Motor Carrier Claims, Sixth Edition, a book from Fried Goldberg LLC, about the complexities of truck accident litigation. Plaintiff’s attorneys can request a complimentary copy. If you have any questions and would like to speak with an Atlanta, Georgia trucking accident attorney, contact us today. 

Previous Chapter: XIII. Other Types of Accidents Related to Commercial Vehicles

Next Chapter: XV. Cellphone Evidence

In most commercial accidents, it will be necessary to retain the services of an accident reconstructionist to inspect the scene and vehicles and download any electronic information contained in the vehicle’s systems. It is important to understand some of the basic principles involved in accident reconstruction to make sure your expert has what he needs to reach his opinions and to determine if his opinions make sense and comply with physics and accepted principles of reconstruction.

A. Skid marks and Physical Evidence at the Scene

Because skid marks disappear from the roadway within days of a collision, it is important to have the accident reconstructionist go to scene and preserve the physical evidence on the roadway within a week of the accident if possible.

The accident reconstructionist should take photos of all the marks and physical evidence left on the roadway and survey the scene in order to create a scale diagram of the area. If the accident occurred more than a month before the lawyer is retained in the case, there is no reason to rush to have the accident reconstructionist survey the scene unless the accident occurred in a construction zone where the layout of the area may change. After a month, there is no chance of the marks being present in the roadway unless it is a very rural and untraveled area.

B. Area of Impact

The area of impact is normally determined by the presence of a gouge mark. When two vehicles collide, one of the vehicles is normally pushed down causing a scuff mark or gouge mark as the metal frame digs into the asphalt.

If there is no gouge mark, then the next method of determining the area of impact is to look at the debris field. When two vehicles impact, there is normally a debris field of broken glass and metal in the area.

While it is not as definitive, the debris field can be used to locate the general area of impact between the vehicles.

C. Lights on the Vehicle

In nighttime collisions involving a disabled or slow-moving vehicle, there is often an issue as to whether to not the lights were on the vehicle that was struck by the tractor-trailer. If the vehicle has LED lights rather than normal halogen headlights, then there is no way to know if the lights were on at the time of the collision. However, halogen lights and electric bulbs (which are the typical lights used on a vehicle) have a filament that can be used to determine if the lights were on at the time of the collision. When the lights are on, the filament is warm and has the ability to stretch in a collision instead of breaking. If the filament is stretched, then the lights were on at the time of the collision. If the filament is cold and breaks in the collision, then the lights were off. The blinking of hazard lights are enough to warm the filaments and so the same rule is applicable to whether or not hazard lights were activated and blinking at the time of the collision. Your accident reconstructionist should photograph all the bulbs and filaments on the vehicle if there is an issue as to whether or not the lights were on at the time of the collision.

D. Electronic Control Module

The Electronic Control Module (ECM) is the “black box” of the tractor and should always be downloaded. The ECM data is so important that we have an entire section of the book dedicated to understanding the ECM data. Make sure your reconstructionist downloads the ECM or obtains a copy of the download from the defense side to interpret the data.

E. Airbag Module on Client’s Vehicle

While we always want to download the ECM from the tractor-trailer, it is also important to locate your client’s vehicle and download the airbag module. If the vehicle is equipped with an airbag module, there is a possibility that the collision could have activated the airbag module and recorded data for the seconds leading up to the collision. The airbag module can record the speed of the vehicle and whether or not the brakes were activated for up to 5 seconds.

Like with the ECM, the data from the airbag module has to be interpreted by the reconstructionist. The zero point on the airbag download does not necessarily mean the point of impact. The zero point is only where the airbag module first woke up and started recording data, and the reconstructionist needs to take into account the type of collision and the physical evidence at the scene to see where in the process that the airbag module would have woken up.

F. Speed and Distance Analysis

The speed of a vehicle can be calculated using the standard formula:

speed = the square root of 30 x distance x coefficient of friction.

The coefficient of friction represents the amount of friction on the roadway. The most accurate way to determine the coefficient of friction is to drag a sled on the roadway which records the amount of friction. However, it is generally accepted that highway asphalt has a coefficient of friction in the range of 0.70 to 0.75. Distance is the amount of distance that the vehicle travelled from the time of braking until it comes to a stop. Normally this is determined by the length of the skid marks left by the vehicle. The speed analysis is only relevant if you cannot determine the vehicle’s speed from the download of the airbag module or the ECM. The electronic data is much more reliable than skid mark measurements and a speed analysis based on skid marks.

G. Perception/Reaction Time

A reconstructionist should be able to use a speed and distance analysis along with perception/reaction time to determine where vehicles were at certain times prior to a collision and if there was sufficient time to take evasive maneuvers or avoid a collision. In a regular daytime scenario presented to a driver, a standard perception/reaction time is 1.5 seconds. The 1.5 seconds includes 1 second to see and perceive the danger and .5 seconds to move the foot to the brake and press it or to make an evasive maneuver. With a tractor-trailer driver, the perception reaction time is 1.75 seconds because there is a .25 second delay from when the brakes are pressed until the brakes actually engage on a tractor-trailer because of the air system that controls the brakes. A reconstructionist can determine where a tractor-trailer was prior to a collision by determining its speed prior to braking and moving the tractor-trailer backwards 1.75 seconds for perception/reaction time (for example at 55 mph that is 88 feet per second for a total of 154 feet). The importance of determining the location of vehicles prior to impact is to see if the truck driver was distracted so that he did not perceive and react to the danger in a reasonable manner (for example if the car was visible in the roadway for 1,000 but the truck driver did not perceive the vehicle until he was 500 feet from the vehicle, then there is a question as to why he did not see it sooner and slow down).

H. Re-Enactments and Simulations

Many accidents involve a tractor-trailer that is across the roadway either while making a turn or disabled for some reason. The claimant’s vehicle collides with the tractor- trailer because the claimant fails to see the tractor-trailer in time to avoid running into it. These types of accidents always involve issues of visibility, especially when the collision occurs at night. The primary defense is that the claimant should have been able to see and avoid colliding with the tractor-trailer if the claimant had been paying attention while driving. As a result, it is imperative to re-enact the collision so that the jury can visually understand that anyone in the claimant’s position would not have been able to recognize the tractor-trailer in time to take evasive action.

We performed a re-enactment of a collision where a tractor-trailer in a rural area was backing into a driveway when the claimant ran into the rear of the trailer which was in her lane of travel. By looking at the photographs of the re-enactment, it is evident that the tractor’s headlights gave the appearance to the claimant that the tractor-trailer was approaching the claimant in the opposite lane of travel, and that it was impossible to see the trailer in the roadway until the claimant was less than 80 feet away.

At 55 mph, the claimant traveled 88 feet in one second. Because a driver’s perception/reaction time is at least 2 seconds at night, the claimant had no chance to perceive and react to the trailer before she collided with it. The re-enactment was critical to explaining this issue to the jury.

Practice Pointer

Always consider a re-enactment of a nighttime driving accident.

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