The Application and Reliability of Commercial Vehicle Event Data Recorders for Accident Investigation and Analysis

Electronic control modules (ECMs) are the most common type of event data recorders being installed on heavy duty trucks. The ECM controls electrical and mechanical systems on the engine while monitoring other vehicle systems. Some of the data collected and stored by ECMs can be of value in accident investigation and analysis even though these reports may not have been originally intended for this purpose. This paper discusses the specifics of data collection from the various ECMs and the reliability of such data when used for the purposes of accident analysis based on testing. A method was developed for applying the ECM data in order to assist in developing an accurate position-time history of the truck. For the study, a tractor-trailer combination equipped with a diesel engine with an ECM was used for multiple straight-line braking runs. A total of 18 different runs were considered, at 30 mph and 60 mph, on both wet and dry asphalt and in both loaded and unloaded conditions. Results suggest that it cannot be assumed that brake status is sampled at the same point as the speed was in the same reporting interval on an incident report. At speeds under 5 mph in the last non-zero reporting interval, the tractor trailer may be stopped even though a speed is shown. A wider range of wheel slip can be expected on an antilock brake system-equipped tractor during maximum braking effort, with the average wheel slip on an unloaded tractor-trailer combination being higher than that of a loaded tractor trailer. The findings also indicate that it is possible to calculate a range of values for the distances traveled to develop a position-time history of a tractor-trailer during a hard brake event.