Ramp metering system improved delay by 25 percent and reduced crashes by 22 percent per ramp meter in Auckland, New Zealand.

Evaluation of SCATS Ramp Metering System.

Auckland; New Zealand

Summary Information

Ramp metering seeks to optimize freeway operation and eliminate or reduce the duration of congestion by regulating access to the mainline traffic lanes. However, ramp metering can cause three problems: formation of traffic queues on metered ramps, on-ramp queue spillback, and off-ramp demand increase. This research focuses on mitigating these problems through the deployment of multiple methods that work together. These methods are based on the SCATS (Sydney Coordinated Adaptive Traffic System) Ramp Metering System (SRMS).


Roadside controllers are installed on motorway on-ramps and are used to (a) set the traffic signal times, (b) set the state of on-ramp changeable signs (c) manage the ramp switch-on and switch-off sequences and (d) measure traffic states using vehicle detectors. Metered flow rates are determined by the local traffic signal controller or by the central control server. Metering rates can be determined by time-of-the-day based operation or adaptive operation. The adaptive operation optimizes mainline traffic by using real-time data from detector stations. The adaptive operation determines control actions at regular time intervals and in this application applies the following functions simultaneously: coordinated ramp metering, feed-forward disturbance compensation, and integrated ramp metering.


On average, at each ramp site, the SRMS annual benefit yield includes a reduction in 26,000 hours of delay (25 percent improvement) and a reduction of 6 crashes (22 percent improvement). This corresponds to an estimated annual cost reduction of AU $2M per ramp meter.

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SCATS Ramp Metering: Strategies, Arterial Integration and Results

Author: Aydos, J. Carlos; and Andrew O’Brien

Published By: Paper Presented at the IEEE 17th International Conference on Intelligent Transportation Systems

Source Date: 10/8/2014


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Goal Areas


Typical Deployment Locations

Metropolitan Areas


ramp meters, traffic management, traffic metering, ramp metering, ramp control, SCATS, SRMS, Sydney Coordinated Adaptive Traffic System, SCATS Ramp Metering System, ramp metering system

Benefit ID: 2018-01236