Safety-Based Volume Warrants for Right-Turn Lanes at Unsignalized Intersections and Driveways on Two-Lane Roadways

Abstract

Safety-based volume warrants for right-turn lanes (RTLs) at uncontrolled major-road approaches to intersections and driveways on two-lane roadways were developed based on traffic crash and conflict analyses. Crash analysis was carried out based on statewide historical data of traffic crashes reported on Minnesota’s two-lane trunk highways. Conflict analysis was carried out using field data and twelve individual VISSIM models involving 350 scenarios to simulate the conflicts caused by right turns for a wide range of conditions. Each scenario involved twenty simulation runs, and each run used a different random seed. Model calibrations involved replication of spot-speed and time-headway distributions observed at field, whereas the model validations involved comparisons between simulated and observed conflicts. Crash-conflict relationships were developed in terms of crash-conflict ratios (CCRs) and crash estimation factors (CEFs). The estimated mean CCRs were