Problem assessment refers to the process by which the traffic safety problems of trucks and buses are discovered and studied. Two approaches to assessing traffic safety problems may be identified: prevalence and risk. Prevalence is simply the frequency with which a traffic safety problem occurs. Crash data files are sufficient by themselves for researchers interested in prevalence. For example, according to the National Highway Traffic Safety Administrationa..s "Traffic Safety Facts, 2002," 4,542 trucks were involved in a fatal crash in 2002, compared with 27,102 passenger cars. Risk, in contrast, is often expressed as a probability or a rate. Risk might be calculated as the chance of a certain outcome given involvement in a crash or as the number of crashes per some measure of exposure, often vehicle miles traveled (VMT). Risk as a metric for traffic safety problems can paint a very different picture from prevalence. In 2002, the fatal crash involvement rate for trucks was 2.12 per 100 million VMT, while the rate per 100 million VMT for passenger cars was 1.68. In this section of circular E-C117, the major sources of crash and exposure data that are available to assess truck and bus safety problems are discussed. The primary goal is to provide the reader with a good foundation in the range of data available, an understanding of the strengths and limitations of each, an introduction to some new sources of traffic safety data, and a list of data needs for future research.
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