COST-EFFECTIVENESS EVALUATION OF TURNING LANES ON UNCONTROLLED APPROACHES OF RURAL INTERSECTIONS. FINAL REPORT

Turning lanes are provided on uncontrolled approaches of rural intersections to improve the safety and efficiency of traffic operations on these approaches. However, there are no generally accepted guidelines that define the circumstances under which the costs of these lanes are justified by the benefits they provide. The objectives of this research were: (1) to evaluate the safety and operational effects of left-turn, right-turn and fly-by lanes on uncontrolled approaches of intersections on rural two-lane highways; (2) to develop a methodology for evaluating the cost-effectiveness of these lanes; and (3) to use this methodology to develop guidelines for the cost-effective use of these lanes. The formulation of the cost-effectiveness methodology was based on a benefit-cost analysis approach. The benefits considered were the accident and operational cost savings provided by the turning lanes. The costs were those of constructing and maintaining the turning lane. Turning lane evaluation forms were designed to facilitate the implementation of the methodolgy. An analysis of intersection accidents on rural two-lane highways in Nebraska was conducted to determine the safety effects of the turning lanes. A computer simulation study was conducted to determine their operational effects. The results of these studies were incorporated into the cost-effectiveness methodology. The cost-effectiveness methodology was used to develop guidelines that indicate the volumes at which the turning lanes are warranted. Their development was based on conditions and costs that were intended to be representative of those at intersections on rural two-lane highways in Nebraska during 1983.