This study examines the relationship of heavy truck mechanical condition and crash risk, using the Large Truck Crash Causation Study (LTCCS). Two specific hypotheses are tested: The first hypothesis is that trucks with defects and out of service conditions are statistically more likely to be inthe role of precipitating a crash than trucks with no defects or out of service conditions. The second hypothesis is that defects in specific systems, such as the brake system, are associated with crash roles in which those systems are primary in crash avoidance, and that there is a physical mechanism that links the vehicle defect with the crash role. Post crash inspections showed that the condition of the trucks in the LTCCS is poor. Almost 55 percent of vehicles had one or more mechanical violations. Almost 30percent had at least one out of service condition. Among mechanical systems, violations in the brake (36 percent of all) and lighting system (19 percent) were the most frequent. Both driver and vehicle factors were found to contribute to crashes. A brake out of service (OOS) condition increasedthe odds of the truck assigned the critical reason (identifying the precipitating vehicle) by 1.8 times. Both hours of service (HOS) violations andlog OOS violations increased by a larger amount—2.0 and 2.2 times respectively. In rear-end and crossing paths crashes, brake violations, especially related to adjustment, increased the odds of the truck being the striking vehicle by 1.8 times.
Abstract