Examining Optimal Sight Distances at Rural Intersections

Friday, November 15, 2019 - 18:15

Decisions made regarding driver sight distance at rural intersections are complex and require considerations for safety, efficiency, and environmental factors. Sight distance, cross-traffic velocity, and vehicle placements significantly affect driver judgment and behavior atthese intersections. A series of rural, two-lane thru-STOP simulated intersections with differing sight distances and traffic speeds were created and then validated by county and state engineers. Experimental data from 36 participants in a time-to-collision (TTC) intersection crossing judgment task and a rural highway thru-STOP intersection driving simulation task was analyzed to clarify the influence of rural thru-STOP intersection characteristics on driving performance and decision-making. Results demonstrated that longer sight distances of1,000 ft. and slower crossing speeds (i.e., 55 mph) were more accommodating for participants attempting to select gaps and cross from the minor road, corresponding with (1) lower mental workload, perceived risk, difficulty, and anxiousness, and (2) better performance in terms of estimated crash rate, and larger TTCs. Second, longer distances of 1,000 ft. appear to aid drivers’ responsiveness on the main road approaching an intersection, specifically when another driver on the minor road runs the stop sign. Minor road drivers positioned close to the roadway at the stop sign, compared to standard stop bar placement, tended to help reduce the speed of main road drivers. Overall,results demonstrated a systematic improvement in the performance of both minor and major road drivers with the implementation of a 1,000-foot sight distance at rural thru-STOP intersections.  The full report is available from Minnesota Department of Transportation at https://www.dot.state.mn.us/research/reports/2019/201934.pdf