The objective of this research was to determine the conditions under which the construction of an auxiliary passing lane on two-lane rural highways is economically justified. A conflict-opportunity model was developed which estimates the number of potential passing conflicts with an opposing vehicle that a given traffic volume will generate. By assigning a cost-per-conflict opportunity and adjusting for the length of passing zones available, the passing-accident costs for a given roadway segment were estimated. Based on prior research, a deterministic reduction of this cost was used to estimate the savings that would result from an auxiliary passing lane. The twowaf model was then used to simulate delay and travel speeds for trucks and passenger vehicles for typical highway sections both without and with an auxiliary passing lane. Benefit-cost analysis was applied to determine the average daily traffic (ADT) levels at which an auxiliary passing lane would be economically justified as a function of section length, percent passing zones available, cost per conflict, construction cost, and discount rate.
Abstract