Two-way left-turn lane (TWLTL) medians are commonly used to solve the safety and operational problems on four-lane undivided roadways caused by conflicts between through and left-turn traffic. Although the potential safety and operational effects of TWLTL medians are well recognised, there are no generally accepted guidelines that define the circumstances under which the costs of TWLTL medians are justified by the benefits they provide. The objectives of the research on which this paper was based were (a) to evaluate the safety and operational effects of TWLTL medians on urban four-lane roadways, (b) to develop a methodology for evaluating the cost-effectiveness of TWLTL medians, and (c) to use this methodology to develop guidelines for their cost-effective use. The cost-effectiveness methodology that was developed is presented in this paper. The formulation of the cost-effectiveness methodology was based on a benefit-cost analysis approach. The benefits were the accident and operational cost savings provided by TWLTL medians. The costs were those of installing and maintaining the medians. A TWLTL evaluation form was designed to facilitate the implementation of the methodology. In addition, a sample problem illustrating the application of the methodology is presented.
Abstract