The Commercial Vehicle Safety Alliance (CVSA) is an association of industry representatives, and state, territorial, provincial, and federal government officials in the United States, Canada, and Mexico. The CVSA's goal is to improve commercial vehicle safety. The CVSA concentrates its safety focus on three areas; driver, vehicle, and hazardous materials. Since 1981, the CVSA has developed a set of criteria for each of the three areas that define conditions which are so unsafe that a truck and/or driver should not be allowed to operate. These criteria are known as out of service (OOS) criteria. To check the compliance of motor carriers with the CVSA criteria, a series of road side inspections is conducted by state and local governments. If the driver and/or vehicle are found in violation of the CVSA OOS criteria, they are placed "out of service" until the conditions are completely remedied. Due to criteria growth, the CVSA wanted to examine the OOS criteria in the vehicle and hazardous materials areas. This study, focused on the vehicle portion of the OOS criteria, attempted to correlate commercial vehicle defects to commercial vehicle accidents. For a major portion of this project, actual accident reports from six states of the United States were evaluated. The states and reports were selected via a stratified two stage cluster sampling system. The results were used to form estimates of the proportion and number of commercial vehicle accidents in the United States with a mechanical defect as a contributing factor. In addition to the accident report sampling, other sources were used to establish a correlation between vehicle defects and commercial vehicle accidents. They include literature, national databases, and post-crash inspections. Results from this study show that approximately 4.6% of all commercial vehicle accidents have a mechanical defect as a factor contributing to the accident. Of these, brakes (1.66%), tires (0.45%), couplings (0.38%), load securement (0.37%), and wheels (0.33%) accounted for the majority. A comparison was also made between the OSU study results and the information gathered from other sources. A cost factor was also used to rank the accidents. The sampled accidents accrued $22.7 million in damage to people and property. The underlying assumption is vehicle defects that are strongly represented in accidents and accident damage estimates should have a strong representation in the out-of-service criteria. / Graduation date: 1997