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#HIGHWAY TRAFFIC DRIVERS#
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Further InformationĮasyWay ITS Deployment Guideline TMS-DG03 Ramp Metering Available for download at:

#HIGHWAY TRAFFIC DRIVERS#

Ramp metering is not deployed to directly deter drivers making short trips but can have the added benefit that it may discourage drivers who do make short trips – from using the motorway network when suitable alternatives exist. More advanced ramp metering algorithms are even more effective. There is a disbenefit to traffic queuing on the ramp but the delay incurred at the signal is offset by the benefits to mainline traffic, both upstream and downstream where the merging traffic is included. Motorway mainline speeds may be increased by as much as 50%. By spacing out the merging traffic, there is less queuing in the acceleration lane and smoother merges, which permits more stable flow and increases overall throughput. This can be regarded as paying a small “time toll” in order to enjoy the benefits of a relatively free-flowing motorway. Ramp metering systems have proved to be a very effective way of maintaining good levels of service for traffic on the motorway, at the expense of those vehicles waiting to enter. The set of occupancy rates are optimised at the area-wide level. One co-ordinated solution (ALINEA in France, for the Paris ring road and Île-de-France motorways) consists of imposing target downstream occupancy rates on the motorway for each of the local metering systems. More sophisticated systems account for conditions over a long section of the motorway, not just at the individual interchanges.

Most of the ramp metering systems that have been deployed are based on demand/capacity or occupancy rate algorithms and are not coordinated on an area-wide basis. Ramp meters may be deployed individually or in combination as a dynamic system. In practice, ramp metering systems are located upstream of recurrent bottleneck congestion points – and have a safety role in addition to relieving main-line congestion. holding capacity on the access ramp to ensure that vehicle queues do not disrupt traffic on the surrounding arterial road network.a traffic monitoring system (automated with several sensors) to determine current traffic flows on the main carriageway and traffic demand on the access ramp.signs informing users of activation – or impending activation – of the ramp meter.control signals (which can be two-light or three-light) located towards the end of the access ramp before the main carriageway, activated during peak periods.Access can be regulated in isolation (each ramp regulated independently) or centralised, with the flows admitted at consecutive ramps being computed by a comprehensive traffic management system. Timing of on-ramp traffic signals is generally dependent on the prevailing traffic conditions on both the main carriageway and the on-ramp. It is important to have sufficient capacity for queuing vehicles so that the adjacent motorways and access roads are not disrupted by queuing traffic waiting to merge. The signals control the discharge of vehicles from the on-ramp, holding back the merging traffic and breaking up platoons of vehicles as required. Ramp metering is implemented by installing traffic signals on the on-ramps to regulate the flow of traffic joining the motorway during peak or congested periods.

monitoring and managing the merging traffic to achieve an even distribution and avoid large platoons of vehicles entering the motorway at once, which increases the risk of flow breakdown.

regulating the flow of additional traffic onto the motorway that, if unchecked, would trigger flow breakdown and lead to critical shockwaves.

One goal of metering is to encourage diversion of short-distance trips off the motorway. The aim of ramp metering is to prevent or delay the onset of flow breakdown, to maximise throughput. Once flows become unstable and stop-start conditions set in, there is a significant loss of capacity and queues develop on the motorway due to the volume of traffic.

Ramp meters reduce the likelihood of flow breakdown by preventing traffic levels on the main carriageway reaching unstable levels. Merging traffic is held on the ramp to be released at a rate typically controlled by the volume of through traffic on the main carriageway. Detection is needed on the freeway or motorway both upstream and downstream of the merge point. It is used to a lesser extent in Europe and the rest of the world due to the practical problems of comparatively short motorway on-ramps with limited queuing capacity. Ramp metering is a form of tactical management widely used in North America.