The database includes all trucks, not just commercial trucks. As a result, government and private non-commercial trucks are included. These vehicles are not subject to random urine drug screening regulations and may skew the data. However, over the years as data collection and review has become more consistent the Federal government and industry have come to use this data as an important indicator of commercial truck safety. We believe that the trends established by this data are useful in spite of the potential sources of bias.
Fatal crashes are only part of the commercial truck safety picture.
A representative of the Federal Motor Carrier Safety Administration within the Department of Transportation was consulted to determine whether other commercial motor vehicle safety regulations might have been effective over time in contributing to the observed accident rate decrease. It is unlikely that this requirement had any impact on the accident rate for 1991. It is possible that the 1992 rate was affected to a limited degree. Nineteen ninety-three would have been the first full year affected by the CDL requirement and by then the accident rate decrease was no longer statistically significant. Our analysis does not establish causation.