What is the Truck Black Box?Diesel engines used in large trucks have a computer whose primary functions are to receive inputs from various sensors and use these inputs to control the engine's fuel system. This computer is also responsible for running diagnostics on the engine control system and setting fault codes if problems are detected. This computer goes by different names depending on the engine manufacturer but is generally referred to as the Engine Control Module (ECM).
Some large truck ECM's have an added feature that allows them to store trip data received by the module. This trip-recorder was designed as a fleet management tool allowing trucking companies a way to monitor their drivers, however, the data recorded is also very useful in analyzing the speed and causes of trucking accidents.
In addition to ECM-based trip recorders there are some stand-alone systems that are independent of the truck ECM. These devices are something a large fleet would install on all their trucks. One example of an stand-alone trip recorder is the Rockwell trip-master.
What Vehicles Have A Trip Recorder Function?Many large trucks built in the last ten years have an ECM Based trip-recorder function. To determine if a truck has this device specific information about the truck will be needed. Add-on trip recorders have been available more than twenty years and could be installed on any type of truck.
How are These Data Retrieved?Each system requires a different retrieval tool. Most of the tools are PC or PDA based and act as an interface allowing the PC or PDA to read the module.
Generally the tool is plugged into the vehicle's diagnostic link located under the driver's side dashboard. If the vehicle's battery and wiring harness have not been damaged, the data can be extracted by simply plugging into the diagnostic link. If the battery is discharged or damaged, an alternative 12-volt power source will be needed. A portable jumper-pack is usually used for this purpose.
What Can These Data be Used For?The ECM's trip-recorder function is primarily intended to aid in the analysis of fleet operations and safety. Capturing this data allows an analyst to see exactly how drivers have been operating their trucks and assess the safety and efficiency of their fleet.
The trip-recorder data can also be used in the reconstruction of the accident. A reconstruction generally includes the analysis of vehicle speeds, impact angles, time-distance relationship of vehicles, etc. The most valuable data for reconstruction purposes is the pre-crash speed data. We stress that this data cannot stand alone, and should only be used as a tool to analyze an accident, just as any other evidence would be used. Generally speaking, investigators have a tendency to take this data at face value, but caution is in order.
This trip-recorder evidence can be very valuable and provide a lot of insight into what happened in a collision. However, it must be analyzed in conjunction with other evidence to ensure its reliability. A reconstructionist must properly analyze and have an understanding of what the vehicle dynamics were prior to the collision. Then he must determine whether the vehicle's pre-crash dynamics affected the recorded vehicle speed. He must also know that the vehicle speed data comes from a vehicle speed sensor (VSS) that effectively measures the rotation of the wheels, however, wheel speed and vehicle speed are not always the same. For example, a vehicle that is rolling-over with its tires off the ground, or sliding sideways, or braking hard, would have a wheel speed that is different than its forward speed. These factors have to be taken into consideration to correctly analyze the data.
