Methodology of the Large Truck Crash Causation Study

Abstract

The Large Truck Crash Causation Study (LTCCS) was undertaken jointly by the Federal Motor Carrier Safety Administration (FMCSA) and the National Highway Traffic Safety Administration (NHTSA). The LTCCS is based on a nationally representative sample of nearly 1,000 injury and fatal crashes involving large trucks that occurred between April 2001 and December 2003. The data collected provide a detailed description of the physical events of each crash, along with an unprecedented amount of information about all the vehicles and drivers, weather and roadway conditions, and trucking companies involved in the crashes. Because the goal of the study is to determine the reasons for crashes in order to develop countermeasures, the data collection was focused on pre-crash events. The LTCCS methodology is based on an analysis of associations in aggregate crash data. The crash assessment coding for each crash provides information on what physically occurred in the crash, including the prior movements of each vehicle, the critical event in the crash, the reason for the critical event, and the factors associated with the crash. Factors that increase the risk of crashes operate through physical mechanisms. For example, driver fatigue may result in a vehicle’s drifting across the center line of a roadway and hitting another vehicle head-on. Because the physical way in which the crash occurred is known, statistical tests can show whether a particular “risk-increasing factor” was over-involved in the kind of crash for which a given physical mechanism—for example, head-on collision—is known. Thus, countermeasures for particular crash types or modes of involvement can be targeted by identifying associations of vehicles, drivers, and environmental characteristics with particular crash types or modes of involvement.