SAFETY AND LEVEL OF SERVICE: EVALUATING THE 1994 HIGHWAY CAPACITY MANUAL METHODOLOGY FOR UNSIGNALIZED INTERSECTIONS

A number of methodologies have been employed to determine the operational performance, or level of service, of unsignalized intersections. The latest methodology embraced by the 1994 Highway Capacity Manual uses an average total delay measure as the determinant of level of service. This study compared field measures of delay to the values generated by the 1994 Highway Capacity Software to determine whether the new methodologies produced acceptable results for delay and level of service for two-way and all-way stop-controlled, unsignalized intersections. The relation of safety characteristics to operational performance levels at unsignalized intersections was also investigated. The objective was to create a relationship between accident rate and average total delay that determines the safety of the unsignalized intersection. Other variables were introduced, identified, and incorporated with delay into a predictive model for both two-way and all-way stop-controlled, unsignalized intersections. The findings of this study supported the statement that the unsignalized intersection module of the 1994 Highway Capacity Manual produced results comparable to manual field calculations. Although there was some slight difference between the two delays with regard to specific numbers, the values measured in the field fell within the correct ranges of level of service as determined by the two-way and all-way stop-controlled intersection 1994 Highway Capacity Manual methodologies. A relationship between safety and level of service was also determined. For the range of variables used, this model provided a basic framework for evaluating safety conditions based on the level of service and other selected characteristics at two-way stop-controlled, unsignalized intersections.