Active Traffic Management

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The Highways Agency is piloting this scheme on the M42, junctions 3A to 7, but a recent CBRD poll found 35% of visitors hadn't even heard of the plan. What on earth is it?


Map of affected areaThe Highways Agency (HA) is the organisation responsible for motorways and trunk roads in England. Its brief from the government is to improve traffic conditions through making the best use of existing infrastructure, taking the focus off building new routes. The Highways Agency presently has no plans for any new routes beyond bypasses and on-line upgrades, and has a "toolbox" of schemes to implement with the intention of cutting congestion, including junction improvements and so on.

Its latest invention is Active Traffic Management (ATM), an extension of the "variable speed limits" scheme running on the M25 with great success for several years.

If ATM is a success in its pilot location, on the M42 junctions 3A to 7, it is intended to apply it to a large section of the motorway network.

What does ATM involve?

The test-bed section of M42 is a busy motorway, with extremely variable traffic flows, as it functions as part of a cross country north-east to south-west route, an orbital route for Birmingham and access road to Birmingham Airport and the NEC (National Exhibition Centre). The existing three-lane motorway (six total lanes plus full hard shoulders) will not be widened to increase capacity. Instead, ATM will be installed. This involves:

Loops and cameras

"Loops" (traffic sensors) embedded in the road surface beneath each lane at regular intervals, and large numbers of CCTV cameras, to detect traffic speed and density;

Ramp Metering

Installing part-time traffic signals at entry slip-roads (ramp metering) to control the flow of traffic entering the motorway;

Gantries holding VMS signals

Erecting gantries at frequent intervals above the motorway carrying large electronic Variable Message Signs (VMS) to relay information to motorists;


Installing lay-bys (or in HA jargon, "Emergency Refuge Areas" - ERA's) at frequent intervals alongside the hard shoulder, with space for several vehicles and emergency phones;

Control room

An off-site control room with computer systems linking all the above equipment.

How does it work?

Most of the time the M42 will function as normal, as it does today. As traffic flows increase, the changing patterns in both amount of traffic and its make-up (how many vehicles are passenger cars, HGV's, coaches and so on) are monitored by the loops and cameras.

When traffic reaches a certain level and is in danger of slowing or suffering stop-start traffic jams, variable speed limits are introduced on the overhead gantries, similar to the system on parts of the M25. This improves traffic flow as lower speeds mean traffic travels closer together and more smoothly, meaning the same roadspace can be used by far more vehicles.

Variable Speed Limits

Ramp Metering LightsIf flows increase more, or variable speed limits can't keep traffic moving, ATM steps up and switches on ramp metering. This uses the slip-road traffic lights to allow a few vehicles at a time to join the motorway, preventing congestion caused by large amounts of traffic trying to merge in all at once.

If these measures don't work and traffic is still moving too slowly (or not at all), ATM's party piece is wheeled out. The VMS mounted above the motorway will indicate that the hard shoulder is now open as a running lane. The safe-havens will provide stopping places for those in trouble.

What else can it do?

ATM has other tricks up its sleeve. The overhead VMS can be used for more than speed limits and hard shoulder running: they can be used to close lanes faster in an emergency and warn of hazards ahead. For example, they could be used to warn of a queue ahead, or an accident, not only mentioning where in the road the accident occurred but actually closing the lanes that are affected.

Hard Shoulder Running

Hard shoulder running may also come into use for the M42's schizophrenic traffic flows when there is a major event at the NEC: the hard shoulder may be opened as a coach-only lane to keep slow moving buses headed for the Centre out of the main three running lanes. It could also be used as an HOV (High Occupancy Vehicle) lane open only to those with more than one person in the car.

Real Examples

The ring road around Munich in Germany (A99) uses the hard shoulder as a running lane in busy periods, as does a section of the A9 near the city. Mark Woolley describes the system there:

Generally this seems to run pretty well, but one broken down vehicle can cause everything to grind to a halt. A car stopped in the hard shoulder...caused big tailbacks. Everything in the hard shoulder lane (generally lorries) had to overtake the car. The situation seems dangerous, but the actual traffic speed is low during the peak periods anyway (so much for unrestricted motorway speeds), so it isn't quite as bad as it seems.

See the 'related links' box on the right for more on the Munich system.

The various elements of ATM are all in use, though not necessarily all at once, in the USA. Marnen Laibow-Koser writes:

Here in the States, I don't think we have anything quite as ambitious as ATM. However, I have seen each component of ATM used in congested areas. Using the shoulder as an extra lane during rush hour is common in certain parts of the country (e.g., around Washington, DC), and I am not aware of any major safety concerns that have been raised by this practice. If I were to single out one component of ATM for criticism, it would be variable speed limits. The Tappan Zee Bridge in the New York City area lowers its speed limit during rush hour; I am not at all convinced that this helps traffic move better (though I'd be interested to see actual traffic measurements). ...The Tappan Zee Bridge has 7 lanes, of which the center lane is reversible; this feature was put in in the last 10-12 years or so and seems to have made a great improvement in the traffic patterns.

David has come up against a problem with the system:

I use the M42 at least once every couple of months, and while the hard-shoulder running certainly does keep it moving fairly well, it is very disconcerting when you're trundling along at about 30mph and come across a collision blocking the hard shoulder that the system hasn't picked up. Admittedly I've only met this on one occasion, and it may have only just happened, but I thought the system was meant to immediately close the lane if needed.

Right of Reply

For several years, this part of the page was headed 'safety concerns' and contained questions which, as far as I was concerned, had not been addressed in sufficient detail by the Highways Agency. A representative of the HA recently got in touch and has provided the following responses.

How will traffic already on the hard shoulder be safe if hard shoulder running is started?

The hard shoulder will only be opened as a running lane if it is clear and safe to do so. The opening sequence consists of monitoring the hard shoulder from the control room via the comprehensive CCTV coverage to ensure that the section of the hard shoulder scheduled to be opened is free from debris or stationary vehicles.

This is followed by setting the signals to indicate that the hard shoulder is open for use as a running lane.

Finally further monitoring of the section is carried out to ensure it is being used correctly and that there are no stationary vehicles on the hard shoulder.

Therefore if a vehicle is stopped on the hard shoulder the opening sequence will be aborted and will not recommence until the vehicle has moved or has been removed.

This situation will be monitored by the control centre via comprehensive CCTV coverage and use of on-road services such as Traffic Officers.

Only when the hard shoulder is clear can the opening sequence recommence. If a vehicle stops on the hard shoulder during the opening sequence, then once again the hard shoulder prior to the vehicle will remain closed until the vehicle is removed.

The hard shoulder that has already been opened will remain open to ease the flow of traffic after the stopped vehicle.

The operation of the hard shoulder is broken down into sections. This means that particular sections of the hard shoulder can be opened at any time to relieve congestion. It is not envisaged that the entire hard shoulder along the complete length of the scheme will be opened at the same time.

The hard shoulder will only be a running lane in heavy traffic, but this is the most likely time for accidents to occur. How will emergency services reach an accident with no hard shoulder?

The use of the hard shoulder will only be required prior to the onset of congestion. When the hard shoulder is opened the traffic speeds will have dropped to below 50mph. It is therefore envisaged that if an accident does occur it is likely to be less severe in nature and should not require the attendance of the emergency services.

Should the Emergency services be required to attend, the signs and signals will be set to close the affected lanes and divert traffic out of them. This should free up a lane to allow the emergency service vehicles clear access to the incident.

Being able to open separate sections of the hard shoulder also provides the ability to clear the traffic quickly ahead of any incident, thus allowing the filtering of traffic to proceed quickly.

How will this scheme be implemented on sections of motorway with intermittent hard shoulders (such as parts of M25, M1, M62) without simply widening the road?*

There are no plans currently to install an ATM type scheme on any motorway with intermittent hard shoulders.

What is the view of the emergency services concerning ATM?

The ATM project team have been in extensive consultation with the emergency services. All the local emergency services who we have been in consultation with have offered their support in the delivery of the scheme and the operational regimes.

More Information

You can also read more about ATM in the Highways Agency's own publicity - a PDF version of their leaflet on the scheme is below. The HA also wished to make clear that they are willing to respond to any other queries via the Highways Agency Information Line on 08457 504030 or the ATM website.

PDF File

Active Traffic Management M42 Junction 3a to 7
PDF document (1.1mb) ha_atm_leaflet.pdf
By kind permission of the Highways Agency


The position of CBRD is this:

ATM is a dangerous policy because it incorporates part-time hard shoulder running. Safety concerns should outweigh all road capacity improvements. Hard shoulders were built at such cost to provide empty carriageway space for those in trouble or for emergency services access, and should remain so at all times. The total cost of the ATM trial is not known but should be compared with the safety and simplicity benefits of simply widening the road.

With thanks to Maurice Turner for information on this page.

* At the time this page was written, newspaper coverage was claiming ATM would be rolled out to other motorways including the M25 and M62, which do not have continuous hard shoulders in all areas.