Ramp Metering E-mail

The following E-mail is one I received in April, 2001 from Brian Harbord, who was at the time head of the UK's ramp meter study team:


Dear "Froggie",

I have just found your list of ramp metering sites while surfing the Web looking for photos of US ramp metering sites and thought I could add a bit to the info you have on UK and European systems.

My team are responsible for the development of ramp metering and other tactical motorway control systems within the Highways Agency, which is responsible for operating, managing and maintaining the English strategic road network.  We are curently undertaking trials of ramp metering at six sites on the M27 and M3 motorways near Southampton, with the aim of confirming the benefits of RM and determining which other sites in England would benefit from this control technique.

The first UK trials of ramp metering took place at a single site on the M6 motorway near Birmingham in the late 1980s and were very successful, showing benefits that would pay for the cost of installing the system within a couple of years.  However, trials at a further 5 sites on the M6, intended to confirm the benefits and provide guidance on wider use produced inconclusive results, and a business case could not be made for further sites in England.  The M6 system used loops to monitor traffic flows, portal gantry mounted signals and a complex control algorithm which ran in a central computer to control the signals.  The signals used long (7 second) greens, which released a "platoon" of up to a dozen vehicles, often triggering the flow breakdown that the system was intended to prevent.  Although the M6 signals remained on the motorway throughout the '90s they were little used and were eventually switched off because the control computer was not y2k compliant.  The M6 sites will be re-activated later this year using equipment developed for the M27 trials.

A review of the M6 trials indicated that the failure to confirm the business case resulted from the high cost of the infrastructure, complex algorithm, central computers, data transmission and the use of long greens limiting the effectiveness of control.  In the early 90s, computer modelling of a range of ramp metering strategies indicated that simpler control algorithms, using shorter greens, would be more effective.  These results were later confirmed by practical trials on French and Dutch motorways undertaken by Holland, France and England in a joint EC project.  The use of cheaper infrastructure, standard equipment and roadside computers also indicated that a much better business case could be made for these simpler systems.  The M27 pilot should confirm this by next year, allowing a rollout of ramp metering at 100-150 sites on the English motorway network as part of the UK Government's "10 Year Transport Plan".

The M27 system uses post mounted signals, supplemented by cantilever gantry mounted signals where sight lines are restricted, and standard MIDAS loops and monitoring equipment.  Green times are being reduced with the aim of moving to "one per green" used on the Continent and in much of the USA.  Results from the M27 will be available next year.

In addition to the RM sites in England, there is one site in Scotland (M8), with further sites being considered and Northern Ireland are also looking at installing their first site. The Dutch Rijkswaterstaat has some 20-30 sites already installed on their network, some of which have have been operating for 10 years.  Several German states have pilot sites on their Autobahn network and the Belgians are about to install their first site.  The French had several sites on the Paris inner ring motorway, the Boulevard Peripherique, in the early '90s, but these have recently been removed (RM was not particularly effective because of the very high flows and because merging traffic has priority on the BP).  The French have trialled a "platoon" based RM system at 6 sites south of Paris and are planning to roll out this form of RM at a further 100 sites over the next 3-5 years.  They are also trialling a "one per green" (or "drip feed" system as they prefer to call it since they use a flashing amber signal instead of green) at several sites near Bordeaux.  The UK, Dutch, Belgian, German and French Government's have recently started working together (as part of the EC's Centrico project) to harmonise ramp metering systems within the EC, so that drivers see similar systems in whichever country they are travelling.

Hope the above helps.




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Page last modified 19 February, 2004