Experimental Analysis of a Direct Access Driveway at a Roundabout: Performance with One or More Slip Lanes

This paper studies the performance of single-lane roundabouts with a direct driveway access road, one lane driveway right-out movements only, to allow facility (land parcel) driveway volumes to access directly at a roundabout. VISSIM micro-simulation assessment considers experimental origin-destination (O-D) balanced flow scenarios with three different driveway volumes (low, moderate, high, and compared to no driveway) and with and without slip lane scenarios (no slip lane, one slip lane, and two slip lanes). Simulated right-turning traffic volumes range from 50 to 500 vehicles per hour. Experiment results indicate that average delay of a roundabout is sensitive to changing driveway’s volumes. As expected, results indicate a direct access driveway, which increases the roundabout vehicle average traffic delay. At high driveway’s volumes level, the total average roundabout delay was increased by 50% at a moderate vehicle traffic level and by 71% at a high vehicle traffic level, before oversaturation. The total average driveway traffic delay was also increased by 8% at a moderate traffic level and by 12% at a high traffic level. Finally, this study also suggests that having more than one slip lane, at different roundabout approaches, reliefs total roundabout average delay, provides an efficient direct roadway driveway access, and enhances access management.