Smart motorways: what, how and why | News from Pure Construction

Smart motorways: what, how and why

Designed to improve throughput and reduce congestion, smart motorways are taking off around the world. New technologies, including in the moment traffic monitoring and analysis, are used to try to smooth traffic patterns, increasing the number of cars that can pass over a section of road in an hour and reducing frustrating – and environmentally damaging – stop-start traffic jams. 

How can you spot a smart motorway?

Smart motorways typically: 

  • use the hard shoulder as a traffic lane either all or some of the time
  • have variable speed limits posted on electronic screens
  • have variable warning signs which alert you to dangers and disruptions on your route
  • use over head signs to indicate lanes are open or closed (e.g. if the hard shoulder is in use, or if a lane is shut following an accident)

Do they work?

Highways England opened the first smart motorway in 2006, and after a decade of testing and improvements, considers the experiment a success. They report benefits including: improved journey reliability; a significant reduction in injuries; decreased severity of injuries in accidents; and no fatalities during the period they were studying. This suggests that smart motorways offer strong benefits, both in terms of improving daily journeys – particularly commuting at peak hours – and potentially saving lives. 


How do smart motorways work?

Cameras pointing at the road gather data from multiple points along the stretch of motorway which is being managed. This data is returned to a central traffic management point and analysed by computer software and human operators. Depending on the situation, an automatic or manual message will be displayed to drivers using signs on the motorway. This might be a simple warning such as “Fog ahead” or an alert about congestion further downstream “Queues between J12-14” but can also include opening or closing a lane (including using the hard shoulder as an extra lane) or altering the speed limit. By encouraging drivers to take advance action (“Ooh, I’ll come off at J11 then”), increasing capacity during peak hours by using the hard shoulder, and smoothing traffic patterns by altering the speed limits, the traffic management centre is able to increase capacity and avoid jams. How traffic flow works can be difficult to grasp without using computer models as it doesn’t always operate intuitively – for example, if a car brakes suddenly to avoid some debris blowing across the road, this can set up a chain reaction as each car following has to imitate the one in front even though the debris is long gone. These are called ‘standing waves’ and can last for hours and sometimes cause major jams. 

How to drive on smart motorways

The normal rules of the road apply on smart motorways, including that speed limits are mandatory. This includes speed limits displayed on electronic signs. Closed lanes are indicated by a red X on the overhead gantry. Only drive on the hard shoulder (marked with a solid white line) when it’s clearly indicated that it’s open. Smart motorways have emergency refuge areas every few hundred meters, and these should be used if your car breaks down in such a way that you don’t have time to exit the motorway in the normal fashion. 


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