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

摘要

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 1.413 × 10~(-6) and 0.496 × 10~(-6) at approaches without and with RTLs, respectively. The values of CEFs, determined as a ratio of CCR to the probability of rear-end/same-direction-sideswipe crashes caused by right-turning vehicles, were between 0.900 × 10~(-6) at approaches with RTLs and 2.168 × 10~(-6) at approaches without RTLs. The warrant guidelines, in terms of volume thresholds, were established for intersection and driveway approaches separately through benefit-cost analysis. The thresholds for driveway approaches were 10 to 26% lower.