Determining exactly what occurred during an auto accident is crucial, not just for insurance companies, but for the drivers involved as well, as certain auto accidents can lead to exposure to criminal liability. It's fairly easy to figure out what happened for certain types of accidents, such as rear-end accidents--it is immediately obvious that one car slammed into the back of another car. This is not the case for all accidents, however. Because drivers who are involved in accidents may not always remember exactly what happened--or worse, they may even lie about what happened to shield themselves from liability--accident investigators must figure out what happened themselves by working backwards and reconstructing the accident based upon the evidence that is available to them.
Who Investigates Car Accidents?
When police become involved in accident investigations, it is normally to deduce whether any criminal actions occurred during the accident. This type of investigation is especially common when the police suspect that drug or alcohol use was a factor in the accident and for situations involving commercial drivers who may have exceeded their hours of service limits. When accidents are investigated by independent investigators, it is usually because they are hired either by the drivers' insurance companies or the drivers themselves. Independent investigators, unlike police officers, are not looking for evidence of criminal activity; rather, their job is to analyze the causes of the accidents so that insurance companies can determine liability and financial responsibly. Independent accident investigators can often be off-duty police officers, retired police officers, automotive technologists, or full-time professional accident investigators.
Investigators want to reconstruct the accident, but in order to do that, they need evidence. This evidence comes primarily from inspections of the site of the accident and inspections of the vehicles involved. The Texas Association of Police Explorers 2 provides an overview of what accident investigators look for when determining exactly what happened in an accident.
Inspection of the Accident Site
When arriving at the scene of the accident, the investigator will gather preliminary information about the accident and what occurred, including:
- The exact location of the accident
- The time the accident occurred
- Who notified the police of the accident and how
- Weather conditions and visibility
- General information as to the seriousness of the accident
- Whether additional support is en route, like tow trucks or ambulances
After preliminary information is gathered, the investigator will assess the accident site. What they're looking for at this stage is point of impact, final resting positions, skid marks, scrub marks, and gouge marks. In order to document these findings, the investigator will use either a sketch or photographs and often both. If the investigator chooses to use a sketch, he or she will note all details at the scene and measurements between each object, including the final resting positions of the vehicles and any debris that may have been scattered due to the accident. If the investigator chooses to use photographs (and most of them do), there are three types of photographs that he or she will take:
Establishing photographs: These photographs show the entire scene, the approaches to the scene, and some sort of fixed object in the background to establish both location and scale.
360-degree photographs: These photographs show all four sides of the accident scene looking north, south, east, and west.
Damage photographs: These photographs are close-ups of the damage to the vehicles themselves and any items that were struck by the vehicles involved.
Inspection of the Vehicles
After sketching, measuring, and photographing the accident scene, the investigator will then inspect the vehicles themselves. The purpose of the vehicle inspection is two-fold; first, it will often reveal unsafe vehicle conditions that could have been responsible for the accident, and second, the damage to the vehicles provides supporting information for witness statements and the investigator's own observations. The amount of damage to the vehicles involved can reveal quite a bit to the investigator, such as how fast the vehicles were going, how hard the drivers braked, and the precise point of impact of the vehicles, among others. The information gathered during the vehicle inspection state is crucial to the final phase--accident reconstruction.
Once the investigator has gathered witness statements and performed the site and vehicle inspections, he or she can then reconstruct the accident. Accident reconstruction is the process of using physics and mathematics to determine the speeds of the vehicles and their relative positions at all times during the accident sequence. Investigator look at a variety of issues to determine this, including the pre-and post-impact direction of travel, the length of pre-impact skid marks, the post-impact distances moved, friction levels for the various surfaces the vehicles traveled on, point of impact, impact angles, and the weights of the vehicles. The calculations that an accident investigator uses will vary according to the accident; for example, a rear-end collision will require a different set of measurements and calculations than a rollover accident.
Let's assume that there is a two-vehicle crash involving one vehicle that was traveling south and another vehicle that was traveling west. When these vehicles collide, physics tells us that they will move in a southwesterly direction--a combination of the momentum from both of the vehicles. If the accident investigator knows how much each vehicle weighs, how far each vehicle moved south, and how far each vehicle moved west, he or she can then use that information to calculate a collision speed for the vehicles. This collision speed can then be combined with the vehicles' pre-collision speed gathered from skid marks to determine the drivers' relative pre-braking speeds.