Vehicle Accident Reconstruction: Is It “CSI For Cars”?

By Jerry F. Cuderman II, Ph.D., P.E.

Editor’s Note: Dr. Cuderman has long been a member of the NMA and a contributor to The Experts Corner, a resource for supporting NMA members. He has been active in the accident reconstruction field for over 20 years, and he wrote this article for our member newsletter, Driving Freedoms, where it originally appeared last year.

The topic of vehicle accident reconstruction (AR) can be of great interest to motorists involved in a collision, especially if criminal charges or litigation is likely.

There are a number of books that go into great detail on how to reconstruct vehicle collisions. Thousands of articles are published by the Society of Automotive Engineers and others on the subject. For the purposes of this article, I will present merely an overview of AR, providing its definition and how it is generally approached rather than attempting to create a primer on how to actually perform AR.

First, a little background on the two arenas in which AR is typically used: Criminal and Civil litigation. In general, there is little difference between AR in criminal and civil cases. The work, time, and money it takes to perform AR is the same. The big difference between the two venues is the level of detail and the funds available.

In criminal cases, the prosecution usually has little or no budget for AR. Therefore, police officers often serve as AR expert witnesses. Unfortunately, very few police officers have the training and even fewer have the time to do a thorough AR. Individual criminal defendants often fund their defense so there may be little money available for AR. The end result is that good quality reconstruction in criminal cases is probably the exception rather than the rule.

In civil cases, plaintiffs’ attorneys are usually willing to spend a reasonable amount of money on quality AR, anticipating reimbursement from a winning verdict. On the defense side, insurance companies usually provide funding; so, again, there is typically sufficient funding for a comprehensive AR to be performed when the stakes are high enough.

AR requires a certain level of work regardless of whether it is for a criminal or civil case and regardless of whether it is a minor fender-bender with low damages or a serious collision with millions of dollars (or serious jail time) at stake.

In fact, minor collisions are often more difficult to reconstruct than major ones because there is typically much less physical evidence produced in the collision. In a minor collision, the police investigation rarely documents physical evidence. Any physical evidence that is produced by the accident is typically long gone by the time an accident reconstructionist is hired.

AR is exactly what its name implies – reconstructing what happened in a collision involving one or more vehicles. My wife likes to tell people that AR is “CSI with cars.” That reference can be somewhat misleading, but, on the whole, it is fairly accurate – particularly in relation to the CSI rule, often heard on the plethora of procedural television series, to “follow the evidence.”

To properly perform AR, one determines what the physical evidence is and works from there. When appropriate, witness accounts are incorporated into the analysis, but eyewitness statements and testimony are almost always discounted when the physical evidence tells you something else. One must always keep an open mind to make sure that the physical evidence is fully understood and that no evidence has been overlooked.

The main steps in AR include 1) obtaining physical evidence; 2) analyzing the physical evidence and witness testimony; 3) forming opinions; 4) generating a report; and 5) testifying at depositions and/or trial.

The first two steps are the most critical. Physical evidence usually includes going to the location where the collision took place and using surveying equipment and cameras to document the roadways, visibility restrictions, signage, and most importantly, any physical evidence still remaining from the collision itself, such as tire marks, gouges in the road surface, and fluid stains from the vehicles.

It is important to note that most vehicles will leave tire marks on the road surface under most conditions during emergency braking even if equipped with an antilock braking system (ABS). The marks may be faint at times and may or may not be documented, but they are often there.

If an accident reconstructionist is hired soon enough after the actual event, much of the physical evidence left by the collision may still be at the site. However, even if the physical evidence is largely gone, there are techniques to reacquire the data if police investigators or others take sufficient photographs shortly after the accident.

Proper photographic techniques are time-consuming and involve using special cameras and/or computer software, but are essential in reconstructing the collision in the absense of key physical evidence.

There are a number of factors that are often analyzed in accident reconstruction (AR): nighttime visibility, visual conspicuity, lamp filament analysis (to determine if vehicle headlights were on at the time of collision), traffic light timing and sequence, roadway friction issues, hydroplaning, mechanical failure, signage, braking performance, and yaw mark (sideslip) analysis, just to name a few. Every collision presents a different set of analysis requirements for AR.

A more recent class of physical evidence involves event data recorders (EDR), often referred to as black boxes. Although the latter term is a bit of a misnomer, more and more vehicles are equipped with a means of recording crash information that is useful in determining what happened. At the very least, typical recording equipment will register information regarding the crash pulse, which is the change in speed of the vehicle during the collision.

Some EDRs will provide up to several minutes of data prior to the collision, including vehicle speed, brake light and anti-lock brake status, transmission gear selector position, throttle position, steering wheel angle, vehicle rotation rates, seatbelt usage, and more.

It is critically important to know how to interpret the EDR data. One of the biggest effects that such data have had is keeping everyone “honest,” since the collected information often provides a solid foundation that cannot be ignored. Hence, the “black box” does not replace AR but can actually enhance it.

On a side note, whether the law says the owner of the vehicle “owns” the data appears to be largely irrelevant – I have never been involved in a case in the past 15 years where access to the data was not ultimately agreed to by the owner or ordered by the court.

AR can ordinarily determine what occurred in an incident without the availability of EDR data.

Analysis of the physical evidence varies from collision to collision. It is almost always necessary to study the physical evidence to determine how vehicles moved prior to, during, and after impact. Estimating vehicle speed is also important and typically requires application of the physics of conservation of momentum and conservation of energy.

Sometimes data from the vehicle are nearly self-explanatory relative to speed and not much else needs to be analyzed. There are also occasions where it is necessary to accurately measure how much a vehicle was crushed during an accident.

That information can then be used in conjunction with government or other crash test data to calculate the energy of the collision itself. Through this process, a complete picture of the vehicle speeds before and after the collision can be developed.

In addition, it is often necessary to perform a time and motion analysis to determine, (1) the relative positions of the vehicles through the course of the accident, (2) what each driver was able to see, and (3) how much time they had to perceive and react to the situation.

Once all the evidence has been gathered and interpreted, it is time to formulate opinions as to what happened in the collision. Driver perception-reaction should be accounted for, and what each person did or failed to do requires analysis to reach conclusions on the ultimate cause of the collision.

Once the accident reconstructionist has formed opinions, it is typically necessary to prepare a report containing conclusions. Many times the AR report is used by other experts – such as the biomechanics specialist who needs to know the speeds and acceleration rates in a collision to determine cause of injury.

Finally, AR specialists are often asked to provide expert testimony regarding the details of their reconstruction. This is usually done by deposition, or if the case goes to trial, courtroom testimony. In a deposition or trial, the AR expert is typically asked how the analysis was conducted and what foundation exists for the opinions rendered.

Twenty years ago, most civil cases probably proceeded until all AR depositions were taken. Then, 95 percent of the time, cases would be settled before trial. Today, more and more cases are settled even before reports are written or depositions taken. One way or another, most cases involving accident reconstruction settle prior to trial.

Editor’s Note: The NMA remains adamantly opposed to the release of EDR data by anyone other than the actual owner of those data, the registered owner or lessee of the vehicle. As we have noted in the past, current federal and state laws are woefully inadequate in spelling out a vehicle owner’s rights with regard to EDR data.

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