Crash Models for Rural Intersections
Four-Lane by Two-Lane Stop-Controlled and Two-lane by Two-lane Signalized
Source: Federal Highway Administration
Three classes of intersection are considered: (1) three-legged intersections with major four-lane roads and minor two-lane roads that are stop-controlled, (2) four-legged intersections with major four-lane roads and minor two-lane roads that are stop-controlled, and (3) signalized intersections with both major and minor two-lane roads. Data was acquired from the Highway Safety Information System, State and Federal photologs, and field work at all intersections. The field work included morning and evening traffic counts by movement and vehicle type as well as alignment measurements out to 800 feet (244 meters) along the major road. The final data sets consist of 84 three-legged intersections, 72 four-legged intersections, and 49 signalized intersections. Other variables collected include Roadside Hazard Rating, number of driveways, channelization, intersection angles, and speed limits.
Negative binomial models -- variants of Poisson models that allow for overdispersion -- were developed for each of the three data sets. Significant variables included major and minor road traffic, peak major and minor left-turn percentage, number of driveways, channelization, median widths, vertical alignment, and, in the case of signalized intersections, the presence or absence of protected left-turn phases and peak truck percentage. Models are developed for all crashes within 250 feet (76 meters) of the intersection center, for intersection-related crashes within 250 feet (76 meters), and for injury crashes. For injury crashes, intersection angle and minor road posted speed are significant. Models of crashes at signalized intersections by approach flows are also investigated, and other model forms are proposed for future consideration.
