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Thursday, 9 February 2012

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Travel and transport

Managing traffic flow at slip roads

Traffic flow on many motorway slip roads is now managed by 'ramp metering'. Find out how ramp metering works and what the benefits are. You can also check whether it has been introduced on the motorways you use.

What ramp metering is

Ramp metering is a way of reducing delays at junctions. It works by managing the traffic on slip roads as they join the motorway.

During busy periods signals break up large numbers of vehicles into smaller groups as they join the motorway. This reduces disruption to merging traffic and reduces bottlenecks.

The system uses signals on the slip road. These start working automatically when traffic sensors on the motorway show heavy traffic moving more slowly than it should.

It can also work in reverse. If the sensors detect long queues on the slip road, the lights can increase flow onto the motorway to prevent disruption on local roads.

What the benefits are

By maintaining a more even rate of traffic flow onto the motorway, ramp metering helps to create:

increased traffic flow during peak periods
less stopping and starting
smother journeys with more reliable journey times

Where ramp metering is being used

Ramp metering was first introduced in England in 1989 on the M6 and was tested for several years. Following the conclusion of a pilot scheme in 2008, ramp metering has now been rolled out across the country.

There are now over 80 ramp metering sites across England's motorway network.

You can see where all the current ramp metering sites are by downloading the map from the Highways Agency.