Experiments were conducted on the john c lodge freeway in detroit to study the effects on freeway traffic of total closure of one or more entrance ramps. The purpose of the experiment was to prove that closing ramps would preserve good freeway operation when headways between vehicles were of the order permitting high traffic volumes at good speeds on the freeway but with no additional capacity to permit ramp traffic to enter. The theory was that, if higher volumes of traffic could use the freeway in a short period of time, there would be less backlog of traffic in the central business area. This would not only benefit freeway traffic, but would actually minimize congestion on the arterial streets. Blankout signals, on overhead or pedestal mounts were used to close ramps. Trail blazer signs were used to mark the alternate routes for motorists not permitted to enter the ramps. Changes in traffic characteristics created by ramp closure were studied on both the freeway and the surface street system. On the freeway, ramp closure resulted in higher volumes, fewer and smaller stoppages and, in most cases, improved average speed. All ramps do not produce equal disruptions of freeway traffic; therefore, by careful selection of the ramps to remain open, widespread areas of a city need not be deprived of an entrance to the freeway. Shifting the freeway entrance point for a relatively few vehicles improved movement throughout the whole area, and these diversions, for the most part, did not stagnate surface street movements. A high percentage of short trip lengths using the freeway was found. The percent of ramp sign violations shows the need for either continuous enforcement or a positive barrier. On the whole, the public acceptance of ramp control was good. Improvements in traffic control on the surface street system would better accommodate bypass traffic, and would reduce complaints.
Abstract