Operational Effectiveness of Passing Lanes on Two·Lane Highways

This report presents an evaluation of the operational effectiveness of passing lanes on two-lane highways in level and rolling terrain. Passing lanes are defined as added lanes in one or both directions of travel on a two-lane highway to provide additional passing opportunities. Passing lanes at intervals on a two-lane highway are a lower-cost alternative to construction of extended sections of four-lane highway. The operational evaluation of passing lanes was performed with a computer simulation model of traffic operations on two-lane highways with and without passing lanes. This model, known as TWOPAS, was validated against traffic operational field data for passing lanes. The TWOPAS model was used to evaluate the effectiveness of passing lanes in improving traffic operations on two-lane highways. The evaluation found that the operational effectiveness of passing lanes is a function of traffic flow rate and passing lane length. Quantitative estimates in the reduction of traffic platooning due to provision of passing lanes are presented in the report. Passing lanes were found to impact traffic operations for effective lengths of 3 to 8 mi (5 to 13 km) of highway, including both the passing lane and the conventional two-lane highway downstream of the passing lane. A case study evaluation of alternative passing improvements was performed using the TWOPAS simulation model; this case study and a benefit-cost evaluation of the results are presented in the report.\n