Many two-lane rural highways are being converted into multi-lane, median-divided highways with partial or no access control. These rural expressways often operate at speeds equivalent to those of rural interstates, but cost much less. This study seeks to provide a better understanding of the safety performance of two-way stop-controlled (TWSC) expressway intersections. A descriptive analysis is used to illustrate how crash rate, crash severity and fatal crash rate are affected by increasing intersection traffic volumes. Next, two safety performance functions are presented for TWSC intersections. These safety performance functions estimate crash density as a function of intersection characteristics. A third analysis uses a safety performance function to estimate the expected safety performance of all the intersections, given each intersection's traffic characteristics. The expected safety performance then is compared to actual performance to determine common characteristics across the intersections with the best and worst actual performance. The data analysis shows that TWSC expressway intersection crash rates, crash severity rates and fatal crash rates increase with increasing minor roadway traffic volumes. This suggests that for interactions at which the minor roadway has a high volume or is expected to have a high volume, engineers should examine the feasibility of special safety treatments instead of designing ordinary TWSC intersections. Preliminary findings suggest that horizontal and vertical curves and intersection skews create problems for drivers trying to judge acceptable gaps in traffic. Designers should thus avoid placing intersections where these conditions exist.
Abstract