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Investigating Tractor-Trailer Accidents

by Eugene G. Beckham and Paul L. Carper

A major tractor-trailer accident usually results in significant property damage, and may involve serious injuries and/or fatalities. Increasing traffic densities and the seemingly ever-present construction zones on today' highways pose increased risks to the over-the-road truck driver, and his or her employer. When a major truck accident does occur, the decisions made by those responsible for investigating the vehicles and the scene can have a huge effect on the financial ramifications resulting from the accident.

A thorough, accurate, and timely technical investigation of the accident can provide important information that will lay the foundation for handling claims in the most effective manner possible. A qualified accident reconstruction expert, and an attorney experienced in defending trucking accidents, are valuable parts of the team that will efficiently investigate and document important evidence that "tells the real story" of how and why an accident occurred.

The purpose of this article is to assist claims handlers and defense attorneys in directing accident investigations and to aid in evaluating reconstruction opinions rendered by others.

Differences between Tractor-Trailer and Automobile Accidents
All vehicles are objects that adhere to the laws of physics according to their mass and velocity, and their interaction with the surfaces upon which they travel. Braking, accelerating, and turning occur as a result of driver input and mechanical function, which controls the forces that the vehicles exert on the roadway. Generally, collisions between "family automobiles," such as sedans, sports cars, vans, SUVs, and small pickups, traveling similar speeds involve similar forces (within an order of magnitude). Properly applied, concepts such as the conservation of momentum and energy can be used to help determine the speed and direction of a vehicle at the time of a collision if adequate information after a collision is available and properly analyzed. In addition, test data of numerous automobiles is available that relates the resulting deformation or crush from a collision to energy. This information can sometimes be utilized to calculate a probable impact speed for a car. A "family automobile" has a relatively constant performance profile, in that altering the amount of its normal cargo does not drastically change the way the vehicle drives. In other words, an automobile will handle, brake, and accelerate substantially the same if its cargo is doubled from having only a driver to adding a passenger. The same cannot be said for a commercial truck.

A modern commercial tractor-trailer is a complex and efficient machine designed for the purpose of hauling cargo, which typically comprises well over half of the total weight of a fully-loaded unit. Federal regulations limit the legal weight of most loaded tractor-trailers involved in interstate commerce to 80,000 pounds, absent a special permit. By comparison, an average automobile weighs 3,000 to 5,000 pounds, with the largest SUVs weighing 8,000 pounds. Therefore, the mass ratio between a truck and an automobile can exceed 20 to 1, which means that a tractor-trailer traveling at highway speed has a great deal of energy and much greater momentum than the average automobile on the road. The behavior of a truck during an accident is quite different than that of an automobile since it is an articulated vehicle with vastly different performance capabilities. The amount of cargo has a significant effect on truck performance, and must be considered in an accident analysis. Factors such as the amount and distribution of cargo affect braking performance. Shifting cargo further complicates the dynamics of a tractor-trailer during an accident. Scientific principles that are generally reliable for describing the motion of two colliding automobiles of similar mass can be so sensitive to slight inaccuracies in approach and departure angles that they are often unsuitable for the reconstruction of a collision involving a tractor-trailer.

Technical, as well as legal, issues arising from automobile accidents have some similarities with truck accidents. However, there are many significant differences. Thus, it is a mistake for a reconstruction expert or a defense attorney to approach a truck accident in the same manner as approaching an automobile accident. The differences must be recognized. The regulations to which a commercial truck and driver are subject require special consideration. A proper investigative team can address issues specific to trucking, will have the resources and equipment available to conduct a thorough mechanical inspection of the vehicles, and will accurately document important physical evidence.

Information Gathering
Physical evidence obtained from the truck(s) themselves and at the scene of the accident can provide valuable information, which if properly analyzed, can help accurately depict what happened. It is important for the accident reconstruction expert to examine the scene as soon as possible after the accident occurs. Accident scene evidence should be considered a "wasting asset," since its condition, and therefore its value, diminishes with the passage of time. Information that is clear soon after an accident will be obscured by traffic, weather, post-accident clean-up and sometimes road repair or construction. Markings in the soil made by a vehicle departing a collision scene, for instance, can deteriorate in mere hours or be lost forever by a careless tow truck, a police car, or a TV/radio news van. Fluid stains on a roadway surface will be spread about by the tires of vehicles passing over them. Tire marks, such as yaw marks, may have a very short life span.

In addition to gathering data about the roadway and the site of the accident, a close examination of the damaged vehicles (including the trucks) is essential. Try to do this before the vehicles are moved from the crash site. Since it is possible that dangling components and other potentially fragile evidence could be altered or lost when the vehicles are towed, the opportunity to carefully inspect them in an undisturbed condition should be pursued. If the vehicles have already been towed to a storage lot, the lawyer or accident reconstruction expert may choose to verify that the vehicles are secure, and make arrangements to examine them as soon as possible after the roadway scene has been documented. The attorney, who should have a working knowledge of issues specific to trucking, typically handles the gathering of witness statements and official reports. Good communication between the attorney and accident reconstructionist is imperative, so that issues of concern identified during the technical investigation can be fully pursued with witnesses. Although most states protect the actions and impressions of a lawyer involved in the investigation of the scene, a lawyer that becomes too involved risks the possibility of being called as a witness. Having an attorney supervise the investigation removes all questions about whether his or her goal was preparing for litigation, or if it was a routine act for other purposes. The lawyer must consider that evidence otherwise protected from discovery may become discoverable if shared with an expert who will later testify at trial.

Scene Investigation
Proper accident scene investigation involves photo documentation and accurate recording of the position of all physical objects in the area of the accident. Even objects that are determined to be irrelevant at the time of the investigation (remnants of other accidents, pieces of uninvolved vehicles, etc.) should be documented to avoid any potential claims that something was missed, and also to be able to later prove why it was not related to the accident. For instance, a set of skid marks within the area of the accident that were from another occurrence could easily be misconstrued by others, and may even be improperly included in official investigative reports. In addition to the skid marks and gouges typically associated with an accident, data such as the resting location of last cargo should be documented, as it may indicate where evasive action or loss of control occurred. Take photographs of the scene with a quality 35mm SLR-type camera. [The use of digital photography is discussed below.] Photographs that may later be used to depict the view of an accident scene to a jury should be taken with a "normal" lens length that closely approximates the angle of view of the human eye.

Accurately determining the position of objects at a major tractor-trailer accident scene is an enormous task for someone not properly equipped to handle the job. Many professional firms and state highway patrol agencies utilize land surveying equipment because of its inherent accuracy and ability to gather large amounts of positioning data relatively quickly. A scale drawing or animation can be accurately produced from the collected data. Typically, a "total station" optical type instrument is used that requires at least two people to operate.

Recent technological advances have made other options attractive for accident scene surveying. GPS surveying equipment offers several advantages: (1) it only requires one person to operate, (2) it is compact enough to fit into a single "carry on" type case, which is convenient for air travel, (3) it has very good accuracy, but requires no calibration, and (4) it records absolute coordinates for each point without need for a reference marker. As the accident scene is surveyed, be certain to have the testifying surveyer-who will later testify-personally mark all findings. Otherwise, it could be argued that someone else (who is not qualified) had interpreted the information and decided what needed to be documented. Truck accidents that occur near an intersection or in a construction zone warrant some additional follow-up investigation to determine whether any abnormal circumstances have played a role in the accident. An official request should be made to the jurisdiction controlling the traffic signals at an intersection to provide records of any recent maintenance or malfunction. In the case of signal lights, the timing plan should be obtained, which can provide valuable information regarding the sequencing of various signals and the associated timing. Many major roadway construction companies will regularly videotape a job site to have a record of warning signs and lights and to monitor progress. Special conditions or deficiencies in a construction site that could be relevant to the accident may, therefore, already be documented. Remaining physical evidence of other accidents, or official records showing an abnormally high accident rate in the area, may indicate a dangerous condition.

Vehicle Inspections
Inspection of the trucks, trailers, and cargo involved in an accident should be carefully performed in order to determine their mechanical condition, the extent and nature of accident-induced or pre-existing damage, the function and usage of passenger restraints, and various other factors. Often, photographs taken by police or adjusters are inadequate, of poor quality and may only indicate property damage to the exclusion of important factors that could shed light on the events of an accident. There is no replacement for being able to thoroughly and systematically inspect an accident vehicle. Minute, but possibly important, facts will usually go unnoticed and undocumented if information from others performing different duties is all that is available to rely upon.

A complete vehicle inspection includes examination of the body, tires, suspension, brakes, lights and steering system for any deficiency or other factors that could be relevant to the accident. Filament analysis of the light bulbs within the area of direct impact can determine which lights were on or off if sufficient shock was received during the accident. Inspection of all seat belts and the general interior of the truck can provide information regarding restraint usage and occupant movement during the accident. The position of all controls, gauges, and switches should be recorded so that the expert can suggest their possible usage at the time of the accident. If a truck maintenance mechanic is asked to inspect the truck, with the possibility that he will later testify, it may be prudent to ensure that the mechanic was not previously involved with the maintenance of the particular truck, to avoid any potential conflicts.

The reconstruction expert should have a good knowledge of photographic techniques so that he or she uses proper exposures and lighting. Photos of clearly marked measuring rules or tapes with color patterns that make measurements easy to recognize from a distance will be of value in later litigation.

The truck accident reconstruction expert should have the knowledge, skills, and equipment to conduct a proper mechanical examination and to determine whether any deficiency with a component could have played a role in the accident. Tractor-trailers employ a complex airbrake system that operates dramatically differently than the typical hydraulic brake system of an automobile. Testing requires that air pressure be introduced into the truck or trailer brake system to enable measurements while the brakes are fully applied, which will provide a basis for calculating braking efficiency. The use of the proper equipment to perform these tasks can have a direct bearing on the accuracy of the efficiency calculation. Simply attaching an air hose from a roadside service vehicle to a truck's braking system can overpressure it and cause component damage, spoliating evidence and creating unnecessary issues.

Keeping Up with Technology
Modern trucks and automobiles rely increasingly on computers to control vehicle systems, and have become more sophisticated as a result. These computers may contain electronic codes that document settings such as the engine governor on a truck; on recent General Motors automobiles, a computer may record speed and other operating parameters (such as brake usage and the percentage of the full throttle applied) for several seconds before an accident. In addition, more and more trucks are equipped with satellite-based tracking and/or communication systems, which record useful data that can help establish speed and position over an extended length of time, thereby corroborating driver logs. With the advent and widespread use of anti-lock brakes, calculating speeds from skid marks is not always feasible, so computers that record vehicle parameters will become increasingly necessary and useful. The ability to recover and analyze this data gives the accident reconstruction expert an independent source of critical speed information that can be vital in determining the events of an accident. Keeping abreast of these rapidly changing technologies will continue to be an important part of the information with which a qualified expert must be familiar. Technical groups such as the Society of Automotive Engineers are a good source of information, and membership in such organizations is a good indicator of the quality of information available to the expert.

Exposing Technical Mistakes and Common Errors
Seldom do all experts in a case reach the same conclusions, especially where accident reconstruction calculations are involved. Some areas of accident reconstruction require reasonable judgment and interpretation. It is therefore not unusual for opposing experts to have opinions that differ. Some opinions may be affected by bias, inferior data, incompetence, improper technique, or intentional skewing of numbers. These problems usually stem from efforts by the expert to promote his or her opinions, but effective cross-examination with precisely crafted questions can reveal the deficiencies.

Here is a typical problem raised by experts who rely on calculations. They may select one certain drag factor and arrive at a single definite result (some even use several digits after the decimal point!). Since the exact deceleration profile of a vehicle is almost always unknown, they should have used a reasonable range of drag or deceleration factors in performing calculations. A sensitivity analysis should be performed to determine how a small change affects the final calculation outcome. It may be determined through proper preparation and careful questioning during cross-examination that an expert's calculations are not robust, and are subject to widely varied outcomes as a result of a small change in input data.

A number of computer software programs are available commercially or freely distributed online as "share-ware" that have the potential of producing accurate measurements. They can calculate speed, simulate vehicle dynamics, and analyze crush factors.

As with all computer programs, the old adage "garage in-garbage out" applies to using computers in accident reconstruction work. Thoroughly examine an expert about the basis for all computer program input, and whether any data was changed during the course of arriving at a final answer. Some of the more complex programs record the number of input changes that are made by the user. Be sure that this information is supplied in discovery if it is available from the program, and ask retained experts to provide this information prior to deposition or trial.

The simple computer programs typically use long accepted basic equations for which the user inputs required data (such as drag factor, distance, etc.) to arrive at a calculated answer. These programs make it very easy to manipulate the output of the calculation by changing the inputs. Programs of this type can also provide a crutch for someone incapable of performing hand calculations. If over-dependence on a computer program is suspected, it is recommended to have the expert work through some basic, but not necessarily simple, calculations on paper. An example would be to ask the time elapsed and the distance traveled for a vehicle to slow from 60 to 40 mph at a constant deceleration rate of 0.5g.

Digital photography has made rapid advances over the last few years. One can now make photographs rivaling in clarity those of 35mm cameras using an equivalent film speed of ISO 50. The cost efficiencies of a camera that uses no film and does not require developing are obvious to heavy users of photography. In addition, the ability to review a photograph immediately after it is taken, and to easily e-mail images is quite attractive. However, being digital, it is also easy to alter the photographic images with a computer.

Since all courts do not or may not accept digital photographs, it is imperative to make conventional "film" photographs to avoid the risk of having digital photographs disallowed or having doubt cast upon their accuracy. The same applies to digital video formats that are becoming more popular as a result of their superior image quality. An increasing number of accident reconstruction experts now rely solely on digital photography.

Many courts do not allow one expert to directly comment on the testimony, qualifications, and opinions of another. So, it is recommended to expose the differences in technique and criticism of analysis through one's own expert during direct testimony. This will allow criticism in closing, or if the other expert is recalled during rebuttal.

Qualifications and Procedures
The accident reconstruction expert should be well qualified, with an appropriate technical background and specialized training for commercial vehicle accidents. A degree from an accredited university in mechanical engineering or a science field is desired. In light of recent rulings, courts are becoming less likely to allow someone with only a law enforcement background to testify about technical issues. Professional registration, such as with a state professional engineering board, indicates an acceptable level of proficiency and holds an expert to a code of ethics. Behavior that is unethical can result in serious fines, suspension, or the revocation of one's registration. Attending relevant technical seminars and maintaining membership in technical societies demonstrates that an expert is making an effort to keep current within the field.

An expert should be familiar with the proper procedures regarding the handling of materials that may become evidence in a lawsuit. When testing or inspection may potentially be destructive, it is necessary to provide notice to the appropriate interested parties before proceeding. At times, physical evidence must be collected to prevent it from deteriorating or being spoiled. Evidence that is secured from a vehicle or scene must be handled, stored, and documented properly. Storage of evidence should be in a facility that offers the protection of a monitored fire and security alarm, and protection from the elements.

The End Product
The results of the scene investigation, vehicle inspections, and witness statements hopefully will allow the accident reconstruction expert to determine facts such as the path and positioning of the vehicles, the sequence of events, actions taken by the drivers, and whether there is evidence of a mechanical problem that could have contributed to the accident. Physical data such as the length of skid marks and the distances that the vehicles travel after collision are analyzed to determine the amount of energy dissipated and thus, their speed at different points during the accident.

The ability to accurately document accident data soon after its occurrence increases the accuracy of an investigation and provides an advantage to an accident reconstruction expert in the objective analysis of technical facts and in reaching more reliable conclusions. This will assist the defense attorney in recommending a prudent course of action to the client.

Eugene G. Beckham is a founding partner of Beckham & Beckham, PA in Miami. He concentrates his practice on the defense of motor carriers and their drivers. He is a member of DRI's Trucking Law Committee and past Chair of the Florida Defense Lawyers' Association Automobile and Motor Carrier Law Committee. Paul L. Carper is a registered professional engineer who has investigated and reconstructed hundreds of vehicle accidents. He is a founding partner of Verite Forensic Engineering, LLC, a consulting firm with offices in Houston and Tampa.

*This article originally appeared in the March 2001 issue of For The Defense and is reproduced with the permission of the Defense Research Institute.

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