Investigating automotive accidents.

Successfully representing victim's of motor vehicle collisions depends on effectively presenting many facts and scientific opinions. Often, the choice of how evidence is presented will be as important as what evidence is highlighted.

When investigating a claim of negligent driving or an uncrashworthy product, counsel should not neglect the opportunity to develop a sound understanding of the facts and dynamics of the collision and the client's injuries. Most of us only vaguely understand how vehicles operate and what exact mishandling or malfunction results in an injury. A brief review of some aspects of vehicle dynamics will help put the investigation in proper perspective.

Understeering and Skid Control

As a vehicle is driven over streets or highways, its weight distribution changes. When the vehicle is accelerating, weight shifts to the rear. When it is decelerating, weight shifts forward.

This weight transfer has a powerful effect on tire performance. As weight transfers onto or off of a tire, the friction between the tire and the road dramatically increases and decreases. When a driver slams on the brakes, the weight of the vehicle shifts forward, and the size of the contact patch of the rear tires is reduced. The reduced friction induces sliding and loss of control.

When a tire rolls over pavement, the friction generated remains steady. This is because the size of the contact patch, the area where the tire meets the road, remains constant. But the slightest steering change sets up relative movement between the tire and the road (sliding friction), and traction decreases.

To reduce the driver's potential for loss of control, most vehicles are designed with "understeer." On these vehicles, the rear tires have better traction than the front tires. An understeering vehicle driven too fast into a curve will tend to go off the road nose first. The average driver can detect and control this movement more easily than the tail-first spin of an oversteering vehicle.

When a rear-wheel-drive vehicle accelerates around a curve, the rear end moves toward the outside of the turn in a classic oversteering configuration. This happens because the surge of power to the rear tires during acceleration causes sliding friction, and the rear tires lose their grip. In a front-wheel-drive car, the sliding friction of the front tires increases; they slide in a straight line instead of gripping and turning.

Skidding happens under many circumstances. A common misconception is that once the vehicle's standard alignment with the road is interrupted, the car is out of control. In fact, skidding can occur whenever a driver locks the wheels by braking suddenly. Skidding occurs when the force of the moving vehicle overcomes-the friction between the road surface and the locked tires.

During a skid, the vehicle may or may not lose alignment with the road. But the distance needed to stop increases dramatically once the tires stop rotating or "lock." The increased time to stop is what causes most accidents where skidding is a factor.

Speed calculations can be made from the length of skid marks. When the distance of the skid mark and the coefficient of friction of the roadway are known, the vehicle's speed at the beginning of the skid can be determined. This assumes, however, that the vehicle skids to a stop rather than stops on impact with another vehicle. The coefficient of friction is a measure of relative slipperiness taking into consideration the roadway materials and the presence of water, snow, ice, and so on.

Investigation Checklist

As lawyers begin their investigation, they should prepare a checklist to coordinate witness interviews with issues or subjects of proof at trial. They should identify the type of exhibits that will illustrate agreement between the testimony of experts and other witnesses. Using this method, they can logically track the elements of proof required:

* evidence of the various events of the collision;

* proof of negligent driving or defective design; and

* testimony to establish the connection between the collision, the design, and the plaintiff's injuries.

Accident scene. At a minimum, if possible, each of the following items should be considered when interviewing witnesses, including rescue personnel and police investigators:

* scene diagrams made by police and witnesses that document the relative positions of vehicles;

* uncropped police photographs of vehicles, roadway, and debris to verify the point of impact and final positions of vehicles;

* site diagram that provides information about the roadway, number of lanes, lane widths, curves, grading, lights, and signs; and

* aerial photographs.

If possible, witnesses should be interviewed at the scene where the collision occurred. Interviews conducted using only photographs can limit witness recollection and perspective. Videotaping interviews at the scene is recommended if information about the crash site will be critical to the outcome of the case.

Another tool to facilitate witness interviews is a scene diagram with an overlay to allow each witness to prepare a sketch of the events. Witnesses should be asked about vehicle speed and direction of travel, accident avoidance maneuvers they observed, points of impact, points of rest, and roadway conditions.

Vehicle damage evidence. Photographic documentation of the vehicle is critical to any expert analysis. Verification of the vehicle's post-accident condition is also essential to chain-of-custody testimony. Witnesses most able to provide this testimony are vehicle occupants, rescue personnel, police investigators, and tow-truck operators.

Types of photographs that will be useful in this area include -

* photos of the vehicles at the collision scene,

* photos of the vehicles kept at storage facilities,

* photos of the interior of the client's vehicle, and

* photos and measurements of an undamaged vehicle of the same make and model as the one that was involved in the accident.

Accident? reconstruction. Selecting appropriate witnesses to give accident reconstruction evidence is critical to presenting the case persuasively. Competent experts range from police officers to engineers with advanced degrees. The experts' level of sophistication should match the complexity of the case.

Illustrative exhibits may be drawings, computer animations, a "storyboard" of illustrations depicting vehicle movements, or photographs of scale-model vehicles shown at progressive positions on a representation of the collision scene.

The reconstruction expert must examine the accident scene to become familiar with conditions of the road at the point of impact and of the road leading to and from that point. Important details include traffic volume, shrubbery that may have decreased visibility, the grade of the road, and its coefficient of friction.

The expert should take photographs of the scene at this time to coordinate with police photographs. Precise measurement can be obtained without the vehicles in place by referring to police photos. Photographs should also show the accident scene as it would have appeared to approaching drivers.

The expert should verify all measurements noted in the traffic accident report. Road widths should be measured; if a painted centerline exists, measurements should be made from it to both edges of the roadway.

Occupant injuries. In many cases, evidence as to exactly what happened to vehicle occupants can be most persuasively presented through the testimony of rescue workers, emergency room personnel, and treating physicians. A bio-mechanical engineer or another forensic engineer specializing in the correlation between force and injury may be critical. While most cases require only a simple approach to keep expenses low and the issues clearcut, crashworthiness cases are more complicated.

The visual techniques to illustrate key points should match the potential value of the case. Juries will pay more attention when television and slide presentations accompany an expert's explanation. The basic goal is to give the jury a visual "instant replay" of the collision and resultant injuries.

Some visual aids used to highlight significant events include -

* side, front, rear, and overhead views of the vehicle interior showing occupant movements related to the overall motion of the vehicle;

* rescue records, emergency room reports, surgical reports, X-rays, and MRI films;

* enlargements, overhead screen exhibits, and slides of pertinent medical records; and

* computer graphics, video-enhanced illustrations, or storyboards depicting occupant movements in the vehicle.

Serious injuries from motor vehicle collisions may include -

* head injuries, which include scalp damage, skull fracture, extracerebral bleeding, and brain damage. Brain damage may or may not be caused by a direct blow to the head and may not directly correlate to the site of a blow. Brain damage may result from rotation of the head due to violent body motion.

* Spinal cord injuries, which may be caused by compression, hyperextension, or hyperflexion. These injuries are usually the result of poor restraint of the occupant's upper torso during an accident.

* internal injuries, including damage to the aorta of the heart. These injuries are often due to a heavy impact to the chest. A poorly designed seat belt can cause internal injuries by compressing organs during impact.

Human factors. It may become important either to explain mistakes made by a motorist defendant or to rationalize the conduct of a client. This involves the field of human factors.

A driver's control of a vehicle is not absolute. A driver who jabs the brakes hard enough to lock the wheels wants to stop immediately, but the physics of the situation produces a skid. The driver's control of the vehicle depends on perception time and reaction time.

Perception time is the lag between seeing a situation and recognizing it as a hazard. Average perception time for inexperienced drivers has been measured in the range of .75 to 1.25 seconds.(1) If the driver is moving down the road at 60 mph, the vehicle will travel from 66 feet to 110 feet before the driver even perceives a problem.

Reaction time is the time required to decide whether to turn, brake, or accelerate once a hazard has been recognized. Reaction time includes decision making and implementation. The minimum reaction that can be anticipated also ranges from .75 to 1.25 seconds-another 66 to 110 feet.(2) This means that a vehicle traveling at 60 miles per hour will cover a minimum of 132 feet and up to 220 feet between reception of a sensory input and initiation of evasive action. That can be a lifetime.

Selection of experts. Several sources are available to help locate a suitable expert.(3) The best advice is to locate a forensic specialist with training and expertise in the area of controversy expected to be the focus of the case. Sometimes a literature search can be helpful to find experts who have written on the subject.

Traditionally, courts have found that a witness can serve as an expert based on "knowledge, skill, experience, training, or education."(4) To assist the expert in giving testimony, use of exhibits, including slides, photographs, and films, is supported by the Federal Rules of Evidence and has been allowed.(5)

Coherent Picture

The physical evidence, witness statements, and injury information are like pieces of a jigsaw puzzle. They fit together in a unique manner to provide a picture of the motor vehicle collision. All the pieces may not be available and some will be distorted. But there usually is enough information to understand much of what happened. Once the pieces begin to form a coherent picture, the attorney finally is in a good position to evaluate the viability of the case and decide on the legal theories to pursue.

Notes

(1) Paul L. Olson & Michael Sivak, Perception-Response Time to Unexpected Roadway Hazards, 28 HUMAN FACTORS 91-96 (1986); Heikki Summala, Driver/vehicle Steering Response Latencies, 23 HUMAN FACTORS 683-92 (1981). (2) Id. (3) See AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS, AASHTO REFERENCE BOOK; RICHARD M. GOODMAN, AUTOMOBILE DESIGN LIABILITY (1970). (4) See, e.g., FED. R. EVID. 702. (5) See, e.g., FED. R. EVID. 703; Brandt v. French, 638 F.2d 209 (10th Cir. 1981).