SCATS Ramp Metering: Strategies, arterial integration and results

Ramp metering is a dynamic traffic management tool used to eliminate or reduce the duration of congestion on motorways. A ramp metering implementation can present some problems to the adjacent arterial network. One source of these problems is the treatment of motorways and arterial network as two separate areas of control. This paper presents three novel methods for ramp metering. The three methods are aimed at promoting a coordinated, efficient and integrated ramp metering approach. These methods are integrated in the Sydney Coordinated Adaptive Traffic System (SCATS) Ramp Metering System which currently controls the largest southern-hemisphere ramp metering network. The achievements of these methods are demonstrated by years of before and after field data from Auckland, New Zealand. An average 25% improvement in both congestion duration and traffic speed is achieved as well as an 8% increase in throughput. A total of 22% reduction in crashes is also demonstrated. Based on average results of 25 surveyed sites, the estimated annual benefits for a ramp metering site are a reduction of 26K hours of delay and a reduction of 6 crashes. In terms of economic value, this results in an estimated annual cost reduction of AU$2M per ramp metering site. These estimates were designed to exclude benefits from any civil works resulting in capacity increases to the motorway network.