Traffic Accident Investigation and Thermal Imaging
By: Detective Larry Wilson
Plano Police Department, Texas
New uses for thermal imaging are emerging more and more as the technology becomes more common place in law enforcement. Thermal imaging technology is proving to be a valuable tool in locating and collecting evidence at crime scenes to include traffic accident investigations.
Traffic accident investigators at the Plano Police Department in
Texas have discovered that using thermal imagers at an accident scene
can help them obtain more accurate skid mark measurements, which aid
officers in determining the estimated speed of the vehicles at the
time of the accident. Thermal imaging can be used to obtain these
measurements because tires generate heat when they make contact with
pavement or other road surface. On most surfaces the thermal signature
of the road will be changed due to the cleaning effect and transfer of
rubber by the tires to the surface. This change to the surface will
remain until it is altered or destroyed (i.e. heavily traveled,
resurfaced etc.). This allows the thermal imager to "see"
skid marks which otherwise are not visible. With this in mind, the
investigator or operator should be most concerned with securing the
crime/accident scene until the evidence can be collected. Also to get
the most accurate picture of the scene, the operator should always
thermal the skid marks backward from where the vehicle came to rest
toward the direction the vehicle was traveling prior to the collision.
Without accurate measurements, it’s difficult for officers to accurately determine a vehicle’s speed at the time of a collision. Another obstacle officers face are antilock brake systems. With antilock brake systems (ABS), a cleaning effect occurs when the brakes are initially applied, which means less rubber is left on the road for officers to make clear measurements during the investigation after an accident. Prior to locking, the brake system grabs and releases, which allows the driver to maintain better control of the vehicle during stopping. This also makes it the most difficult evidence of braking for the investigator to locate without the aid of the thermal imager.
The Plano section of the Dallas Morning News on August 11, 2000 ran the following headline: "Police seek information in fatal weekend crash." The article quoted the Plano Police Department by stating that drag racing might have been a factor in a previous weekend traffic accident that killed one of the passengers, an 18-year-old man. Officers located several feet of skid marks prior to the car hitting a concrete culvert, crashing through trees, flipping over and finally landing in a lawn where it burst into flames. Officers began the task of gathering evidence, which would be helpful in reconstructing what occurred. They hand painted all the skid marks they could visually see along with other points of evidence such as shoes, auto parts that had been torn off the vehicle and personal effects belonging to the occupants. After marking as much as they could see officers requested a thermal unit to check for the heat signature of the skid marks on the roadway that they could not visually see. The operator, Officer Mike Nunns located a total of 46 ½ additional feet of skid marks with the thermal imager, which could not be seen without it. "Speed was the primary cause of this accident. The location of the additional marks will show a faster speed and will be used for the filing of manslaughter charges against the driver," Officer Nunns said.
Thermal imagers have also proven effective in determining which skid marks belong to the vehicles involved in a crash. This is extremely important on a heavily traveled roadway where several skid marks from previous accidents are visible. With a thermal imager, it is easier to determine which marks are related to the most recent accident. In a case that the Plano PD investigated, a cement truck locked up the brakes just before striking a family vehicle broadside as it entered an intersection. It was a heavily traveled intersection where several skid marks were previously present on the asphalt. The imager showed Plano officers which skid marks belonged to this accident. It also revealed that a few marks were missing, which indicated the officers needed to check the brakes on the truck. It was determined the brakes were faulty, which was a huge contributing factor in this accident.
The Plano Police Department has been using thermal imaging technology for several years to aid in the investigation of traffic accidents. The department has yet to be challenged as to the way the evidence was gathered or on the technology itself. The Plano PD will continue to utilize thermal imagers to collect vital evidence at accident scenes and encourages you to do the same.