Photographs documenting the principal direction of force for each vehicle are crucial to the understanding of the dynamics of the before-and-after paths of the vehicles. It is also an important element in determining the kinematics of the vehicle occupants and eventually the biomechanics and mechanism of injury. Besides large crush, very subtle evidence, such as striations and paint transfers, should be included in your pictorial documentation. Detailing evidence of seatbelt use is crucial when analyzing and investigating an accident involving specific types of injuries. All sides of the vehicle should be photographed at an acute and linear position to the plane. Overhead photographic documentation can be done by mounting the camera on a PVC pole with a mechanism to snap the shutter. This overhead method of photography can be crucial if you need to determine the speed of a vehicle at impact from the damage incurred (crush information).

The Outside Counts

Anytime vehicle damage is the predominate method in analyzing a collision, the properties of metal parts must be considered. Stiffness of metals relating to vehicle collisions are an indication of the resistance of a metal at a given angle to permanent deformation or crush. Restitution of a metal is the rebound relating to the angle and force of impact. Both of these values are necessary if an accurate and unbiased investigation and reconstruction are to be performed. Paint transfers, which occur when two surfaces of different color are forced together, creating friction that temporarily melts the paint, can be very subtle or very obvious depending upon the angle and speed at collision.

Another important area relating to vehicle damage includes the matching of roadway scraps, gouges, and scratches with the undercarriage of the vehicle. Vehicles can leave the roadway and strike roadway signs, traffic-signal posts, wooden polls, trees, or culverts. Each one of these impacts usually leaves a distinctive damage profile that aids in identifying the dynamics of the vehicles. The type of damage concerned with absorbing energy and speed determination comes from contact damage as opposed to induced damage. Contact damage is the damage directly caused from contact between two objects. Induced damage is a result of contact damage, such as the bottom of a windshield breaking from the hood being pushed rearward.

Wheel rims and tires can reveal important clues as to how an accident occurred, too. Tires can blowout slowly or quickly depending upon the object they strike. Wheel rims can be bent from impacts with curbs, potholes, or other objects. When tires and wheels are damaged, a thorough investigation should reveal the cause and also the effect on the vehicle itself. For example, if a vehicle leaves the roadway and the driver attempts to recover, the inside edge of the tire usually will have scrape marks if the drop-off of the pavement is approximately four inches or greater. Fluid leaks on the roadway can tell the story of initial and post-impact travel as well as the point of rest. However, be aware that fluid naturally seeks the lowest point of the roadway, so do not assume that pooling fluids indicate the final point of rest.

Vehicle lighting can be crucial when investigating left or right turning vehicles and nighttime accidents. Headlights or turn signals that have one or two filaments can be used to determine what is called cold or hot shock. If a lamp is illuminated, the filaments can reach temperatures as high as 2300 degrees Fahrenheit. If a severe force was applied in this state, the laws of physics would dictate that the filaments would move or bend in the direction of this force. Additionally, according to Rudolf Limpert, author of Motor Vehicle Accident Reconstruction and Cause Analysis, if the glass headlight bulb breaks, the filaments will show signs of oxidation after having come into contact with air. When inspecting a vehicle, it is imperative that the lights are not turned on, since doing so will destroy this type of evidence. If you decide to move the lamps, special documentation and orientation up or down must be maintained. It is possible that, if the glass is broken when the filament is hot, glass pieces will melt and adhere to the filament wires. It should be noted that not all lamps and bulbs have this type of filament.

Useful information also can be obtained by inspecting bumpers and their accompanying structures. Bumpers have thresholds that, once surpassed, result in permanent damage. All bumper systems are not equal and consequently have different damage thresholds. Damage thresholds are much less for barrier crash tests than in real-world, vehicle-to-vehicle impacts. The reason for this is that in barrier impacts, all of the energy is used to damage the crash-test vehicle, while in real-world situations, both vehicles absorb energy from the impact. The structures of bumpers include bumper bars, bumper isolators, frame brackets, and Styrofoam absorbers. Bumper isolators are small shock absorbers mounted horizontally behind the bumper and are intended to take in the energy from impacts before it reaches the frame of the vehicle. By analyzing the distance of movement or collapse of the isolator, one can compare results with tests to determine an approximate value of energy absorbed. With this information, an approximate impact speed can be determined. This procedure must be done for both vehicles; if only one vehicle is inspected, only half of the evidence has been analyzed. Styrofoam bumpers are made to be used one time, since these types of bumpers terminally deform when absorbing energy whereas the isolator will usually return to its undamaged position, if the impact has not surpassed the isolator's threshold.

Take a Look Inside

The interior of a vehicle is just as important to inspect and analyze as the exterior. Usually, interior evidence consists of occupant movements and mechanisms of injury. Occupants always travel towards the impact; if there was a forward impact, for example, all occupants would move towards the front. If the impact is offset, such as 30 degrees from the centerline of the vehicle, the occupants would move towards this 30-degree impact. Windshields can become cracked from various objects, most typically from unbelted individuals. Windshields are now made so that they will not splinter and break in many pieces, which can seriously injure occupants. They are now designed to shatter and usually stay in one piece. Side windows are not designed the same way; shattered glass from these can indicate whether the force came from within the vehicle or outside of the vehicle.

Instrument panels or dashboards used to be very dangerous and produced more injuries at lower speeds than today's designs do. Dashboards and steering wheels today are padded and airbags have been designed to prevent the occupant from reaching them. Seatbelts can be analyzed to rule out use or nonuse by the occupant. Seatbelts that have been used usually show marks on the latching system and stretching or loading of the belt fabric, according to R.W. Rivers' Seatbelt & Air Bag Systems Manual. Injuries compatible with extreme forward displacement are usually caused by not using seatbelts.

Lower areas, such as underneath the dashboards, are another source of serious injuries for unbelted individuals. Typical injuries include fracture of the tibia, fibula, femur, or hip. An investigation of the area is necessary to match up the injuries to the occupant. This type of investigation is most useful when none of the occupants will admit to driving and the possibility of alcohol or drugs is involved. Hair, blood, skin tissue, and injury patterns all tell a story as to the seated position of occupants. An inspection of the vehicle should include measurements from the suspected seating position to the dashboard and steering wheel. This information is necessary to assess seatbelt usage.

With the onset of airbags, injuries have been reduced even more so when combined with seatbelts, but they also can reduce injuries if used alone. Deployment of airbags can give an indication of the Delta-V or severity of the impact. Airbags can deploy at various Delta-V speeds, usually over 14 mph, according to J.C. Marsh IV's paper for the Society of Automotive Engineers entitled, “Supplemental Airbag Systems: Consumer Education and Experience.” Impacts between eight and 14 mph may cause airbags to deploy, though. The direction of impact for proper deployment of the airbags is usually within a range of 30 degrees of either side of the vehicle's centerline.

Seat cushions and seatbacks as well as headrests also are very important when inspecting a vehicle. A properly positioned headrest can drastically reduce injuries such as whiplash. Whiplash occurs when a rear-end impact forces the torso of the occupant forward while the head and neck, still wanting to occupy the same space (inertia), remain stationary. The seatback also plays an important part because of energy absorption as the torso is forced into the seatback and the stored energy is released, propelling the torso of the occupant forward. This force, at times, can be faster than the vehicle itself because of a slingshot effect.

Another area that is important to inspect for side impacts is the glass fragments from the side windows. Matching up occupant injuries to the side door and the center console for a right side impact where the driver may slip out of the shoulder portion of the seatbelt and contact the center console or gearshift should also be done.

Reconstructing vehicle accidents is an important part of properly adjusting an auto claim and can help determine proper liability. By conducting a comprehensive and scientific investigation of the accident scene and the vehicles involved, more often than not, an adjuster will be able to effectively make his case as to what happened.

Dennis Andrews is principal of Accident & Safety Consultants. He can be reached at 856-596-6903.