Effects of access features and interaction among driveways as investigated by simulation

The number, placement, and design features of driveways are important issues in access management. Simulation was used extensively so that the key parameters and variables could be controlled efficiently and so that underlying effects could be studied systematically. Some results were not surprising: deceleration lanes are important, as are acceleration lanes; the presence of driveways has some adverse effect on arterial through-vehicle speed; and the effect is greater as the number of driveways increases. But the emphasis was placed also on the effects on driveway traffic, in terms of driveway per-vehicle delay and queuing. For multiple driveways, the effect on the first (most upstream) driveway of the presence of the others was dramatic. Delay and maximum queue size increased significantly, indicating a substantial reduction in driveway capacity. This reduction was estimated at 30 to 50 percent by an analytic investigation. The effect of adding one downstream driveway was equivalent to increasing the arterial volume by 25 percent in the moderate-to-heavy flow range. Finally, the multiple driveway work revealed an oddity in that the downstream driveway performed better than it would have if it were alone. The authors attribute this to the decreased arterial environment and the "sheltering" effect of the turbulence from the upstream driveway.