Improvements to motorway traffic operations were observed following the introduction of a ramp metering scheme on one of the access slip roads leading to the M6 near Birmingham. Average journey times on sections upstream and downstream of the metered ramp were significantly lower with the scheme in operation, while capacity flows through the downstream bottleneck significantly increased. Journey times for traffic using the ramp were longer under metering, but the additional delays which this produced were considerably less than the overall gains achieved by vehicles on the main carriageway. Since there were no observed adverse effects on the adjacent all-purpose road network, the outcome was a net benefit from the scheme and this was evaluated in economic terms. (A)
Abstract