A Review of the Impacts of the Towaway Reporting Threshold on a Highway Safety Program
Summary Report
Source: Federal Highway Administration (FHWA)
State, County, and Municipal governments are all seeking ways to meet increasing demands on their limited resources. In many cases, the available resources are either shrinking or growing at a slower rate than demand. For this reason, a number of States are in the process of studying, or have studied, the possibility of changing the non-injury threshold to a higher level where at least one vehicle is disabled to the extent it must be towed from the scene -- the "towaway" threshold. This threshold has already become the default standard in some major metropolitan areas, in spite of what the law may require. Some States are even considering an injury threshold for reporting collisions. A 1998 study by Zegeer et al. found that if there were a towaway threshold, only 51.7 percent of crashes would be included and if there were an injury threshold, only 33.7 percent of crashes would be included. They also found that a towaway threshold would: (1) exclude more crashes on urban streets than on rural roads (2) underestimate rear-end, sideswipe, parking, and animal crashes and (3) seriously affect the reporting of run-off-road, angle, and turning crashes. Zegeer et al. concluded that a towaway threshold would seriously affect the ability to meaningfully evaluate roadside safety treatments. Miller et al. (1987) showed that underreporting of crashes to include only towaway, injury, and fatal crashes would result in lost benefits because of the non-optimal selection of safety projects as safety funding increased. Although these studies have investigated the effects of a towaway reporting threshold on fundamental issues related to resulting changes in reported crash types, more information is clearly needed on the effects of a towaway threshold on the State or local safety engineer's use of crash data. These effects include the development of a high-crash priority location listing, the identification of crash patterns for these locations, and the related selection of appropriate crash countermeasures. The purpose of this study was to review the potential impacts of a towaway reporting threshold on the North Carolina Highway Safety Improvement Program (HSIP) listings and on the locations and types of crash patterns identified on collision diagrams by field engineers.
