The experimental expressway traffic control system demonstrate that automatic entrance ramp metering can be a practical remedied for congestion caused by expressway overloading. Excellent motorist compliance with the one-vehicle-at-a-time- scheme of the metering traffic signals enables a significant reduction in expressway congestion by delaying and diverting entrance ramp traffic. Although some geometric restrains and uncontrollable variables are insurmountable with the present control system, significantly higher and safer overall expressway operational levels are provided than without control. A net overall control savings of 256 vehicle-hours of total travel time (296 vehicle hours saved by expressway users; 40 vehicle hours additional delay to metered and diverted ramp traffic) was produced on the best peak periods with and without control. Ramp controls substantially increased upstream expressway flows, without greatly changing downstream bottleneck outputs. Adverse metering effects attributable to ramp queuing and diversion were notice able only at the metered ramp heads; restrictive metering controls tended to promote permanent diversion to alternative routes. In as much as the greatest control benefits are realized when non-congested expressway flows are maintained, the feasibility of extending the present control system to include enough upstream metered ramps to allow the complete prevention of overloading congestion should be investigated. Care just be taken with all practical applications, however, as the degree of ramp control required just not produce adverse effects negating the derived expressway benefits.
Abstract