Active traffic management

Active traffic management (also managed lanes, smart lanes, managed/smart motorways) is a method of increasing peak capacity and smoothing traffic flows on busy major highways. Techniques include variable speed limits, hard-shoulder running and ramp-metering controlled by overhead variable message signs. It has been implemented in several countries, including Germany, the United Kingdom, Canada and the United States.

It is currently in operation on the M42 motorway south-east of Birmingham and in Warwickshire. The scheme had initially been criticised by some due to possible safety and environmental concerns, however a Highways Agency report into the first six months of the scheme showed a reduction in the number of accidents from over 5 a month to 1.5 per month on average. it has now been expanded onto other roads following the initial evaluation on the M42. It is seen as a less expensive alternative to road widening.

The section of road subject to ATM is monitored by MIDAS sensor loops placed in the road every 100 metres (328 ft) (which is closer than normal) to observe traffic flows. A computerised system monitors the traffic flows and can set the best speed limit for the current flow of traffic and switch on speed limit signs mounted on gantries up to 2 kilometres (1.24 mi) before an incident. Operators can also monitor 150 CCTV cameras along the route and can control both the speed limits and information signs. Overhead variable message signs can direct drivers to use the hard shoulder during busy periods.

When the speed limit has been lowered to 60 miles per hour (97 km/h) or below the hard shoulder can be opened as an additional lane. To facilitate this and still maintain safety a series of refuge areas have been created around every 500 metres (1,640 ft) along that stretch of the road. These take the form of lay bys to the side of the hard shoulder and contain SOS phones within them. In the event of a vehicle breaking down on the hard shoulder, operators can close it, or they can close a lane to allow emergency services access to an accident. The hard shoulder is never opened on the sections under a junction between the off and on slip roads. Close to junctions use of the hard shoulder as a lane is restricted to traffic exiting or entering at that junction.

ATM involves converting the hard shoulder into a normal lane during periods of high traffic flow to expand the capacity of the road and may reduce the need to widen motorways. Similar schemes have already been implemented in Europe.

The system makes use of Automatic Number Plate Recognition cameras which to monitor traffic flows and tailor the system. Digital enforcement cameras are also mounted on the gantries and are operated by the West Midlands Police to enforce the mandatory variable speed limits.

While active traffic management is currently limited in Canada, more implementation is expected to occur in the future. The QEW highway near Toronto utilizes ramp metering for a portion of the roadway on-ramps.

The city of Toronto has also implemented traffic signal re-timing (signal optimization). Approximately 22 intersections in Toronto now have adaptive signals.