About Those M1 Variable Speed Signs

Highways England Customer Services have responded to complaints about the operation of variable speed signs along the M1 corridor through Luton.

A spokesperson said, "The signs you describe that you have seen along this route would have been set by our automated system called MIDAS (Motorway Incident Detection and Automatic Signalling). MIDAS uses sensors in the road to detect incidents or congestion and then automatically sets advisory reduced speeds (e.g. 60, 50 40 mph) and warning messages (e.g. Queue Caution) on VMS.

"To help manage busy traffic flow, a variable speed limit and incident detection system has been in operation since 1995. The controlled section is fully fitted with loop detectors, which collect real-time data such as vehicle count, speed, and traffic density. Signal gantries automatically display mandatory speed limits in response to the traffic data recorded by the loop detectors. The speed control system creates an environment to minimise the risk of flow breakdown, reduce accidents which may happen as a result of flow breakdown, and produce more reliable journey time.

"Many years of research have enabled the company to develop techniques and systems to achieve effective traffic control and these systems are constantly monitored and adjusted to maximise benefits and operational reliability. As the traffic demand increases, inevitably we must expect the signals to be on more often and for longer periods. The signals and message signs can also be manually set by the Police or Company staff to complement or override automatic settings.

"Drivers may not realise why these signals are set, and this is understandable as there may be no apparent reason for the settings. However, the system is detecting high traffic demand and is using the signals to prevent the congestion from deteriorating into flow breakdown.

"Incident settings are designed to protect stationary/slow moving vehicles and the back of queues that can result from these. The incident detection system also works alongside the congestion system to control the speed of traffic in congested areas where flow breakdown has already happened.

"The whole system is dynamic and responds minute by minute to the current conditions anywhere on the controlled section. The whole section is linked together to enable staged and smooth changes to the signals throughout your journey. The signal system is intelligent and prevents the signals changing the limits displayed or switching the signals ‘on and off’ too quickly. This gives drivers time to respond and ensures the signals are not confusing. Once the signals are on, timing delays are introduced to stop signals switching off prematurely. Studies have shown that after heavy congestion has occurred, it is vital to control the recovery of traffic speeds and let the traffic flow recover safely. This minimises the risk of further flow breakdown or traffic incidents re-occurring.

Facebook discussion with annonymised names to protect the innocent:

"I notice that one of the comments mentions the reduction of the speed limit due to air quality levels. This refers to the section between junctions 28 and 35a, where there is a 60mph limit which is in place for five hours a day, at weekday peak times (07:00-09:00 and 15:00-18:00). We expect the speed limit will be in place for as long as it is required for maintaining air quality levels. As engines improve, particularly diesel engines, we hope that the peak time speed limit can be lifted. The 60mph speed limit won’t improve air quality in this area, but it does mean that air quality won’t reach illegal levels."

If you have any further questions regarding this or any other Highways England issue please feel free to contact via our 24 hour Customer Contact Centre on 0300 123 5000. Alternatively, please e-mail info@highwaysengland.co.uk  or access our website http://www.highways.gov.uk where information on all Highways England policies and procedures can be found.


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Luton local news and events for the town of Luton, Bedfordshire, UK. Editor Alan Winter.