The Practical Implementation of Ramp Metering

Ramp metering is a traffic control measure used to reduce traffic congestion by regulating the flow onto the main carriageway from the entry slip roads. Based on the results of a pilot ramp metering scheme, the HA decidedto take forward many of the proposed improvements, and to implement 30 sites across England by March 2007. Understanding traffic behaviour is paramount to the successful management of the traffic flow on the motorway under peak traffic conditions. The four algorithms used in a ramp metering system are: release algorithm to convert the required ramp flow to actual ramp flow by the setting of traffic signal timings; arbitration algorithm to choose the correct ramp flow (from the various control algorithms) to sendto the release algorithm; algorithms which produce required ramp flows tocontrol main carriageway; and data filtering algorithms to process the data from the main carriageway (MCDF) and the ramp (RDF) to provide inputs to the control algorithms. Experiences from the pilot study showed that ramp metering is only suitable for installation at certain sites. The initialresults show that ramp metering can provide significant reductions in journey times on the main carriageway. The evaluation of journey times on theslip road, which is on-going, has revealed difficulties in measuring accurately the delay imposed on vehicles which at height of the peak times canbe in a moving queue on the slip road, waiting to join the main line carriageway via the ramp metering signals. Further improvements to the system are currently being investigated, based on the lessons learned from the implementation. For the covering abstract see ITRD E134522