Collision Investigations with a Thermal Imager

We're pretty lucky at work. During daylight hours, we have a traffic unit that handles the majority of the motor vehicle collisions (MVCs). Being a third shift guy, that doesn't help me a whole lot, but in my section of the city, we don't get a ton of MVCs. We catch most of our drunk drivers before they hurt anyone, so I really don't have to investigate too many collisions. Also, if there is a potentially fatal collision, we have a reconstruction unit that takes over the investigation.

However, many agencies aren't as lucky as we are. Or, you may be one of those people (and no, I don't mean one of those people) who investigates collisions on a regular basis. If you are an investigator, either by choice or by necessity, you may find a number of situations where a thermal imager can assist you.

Rescue or Recovery?

A Kentucky fire department shared a very illustrative story with me. Their ambulance was returning from the hospital, driving along the interstate. The firefighters noticed a new break in the guardrail near bridge. When they stopped to investigate, they discovered a vehicle upside down in the creek below. Water was up to the tires.

The firefighters' first reaction was to dive in and attempt a rescue. They called for assistance and performed a quick size-up of the situation, aided by a thermal imager. They learned that the bottom of the vehicle was relatively cool. Since a vehicle that leaves an interstate will have a hot engine, exhaust pipes and tires, the thermal image told them that the vehicle had been in the creek for quite some time.

That meant that this was not a rescue situation; it was a body recovery. The advantage here, of course, is that emergency responders did not place themselves unnecessarily at risk. While not every MVC poses such a clear application for a TI, there are a number of more mundane uses for thermal imagers.

Tracking Vehicles and People

Especially in rural areas, it is possible for vehicles to leave the roadway and leave little evidence behind. At night, this can make a 911 call for a possible collision turn into a hunt for a vehicle, much less for victims. A thermal imager can help identify tire tracks, paths and directions of travel.

The tires leave a heat imprint on the asphalt, even with antilock brakes. During a yaw or skid, friction as well as rubber transfer will change the surface of the roadway, leaving a unique thermal impression. Environmental conditions will impact how long these unique impressions are visible on the TI, but they will allow investigators to identify the path of a motor vehicle, as well as where it may be off the roadway.

Just as vehicles can be lost off the roadway, so can occupants. Subjects thrown from vehicles can be difficult to locate at night, especially in denser foliage. A quick scan with a thermal imager, however, can help identify where potential victims may be. Their body heat should radiate to the TI, serving almost as a beacon to the rescuer.

Measuring Skids

Just as the TI can track the direction of travel for a vehicle that leaves the roadway, it can also help measure the length of a skid. This task is even hard on those of us who investigate now that antilock brakes are so common. But what is hidden from the eyes is not hidden from the TI.

Again, since the tire is still imparting heat and rubber to the roadway, even though it is not leaving a major skid mark, the tire creates a new thermal image on the roadway. In personal experiments, I have examined skid marks at speeds of 30-35 mph. I was able to add four or five feet to each skid mark with the TI, compared to the skid mark that was visible solely to the eye. I've heard of officers adding 15 or 20 feet to a skid.

Those of you who specialize in collision investigations know how valuable an accurate skid measurement can be to your estimation of speed. Just think about the results when you can see the true start of the skid...and add distance to the final measurements.


A thermal imager can help at various stages of a MVC. It can help locate the collision, identify the number of vehicles or passengers, as well as track the length of skid marks for the investigation. Each of these makes our jobs as police officers easier.