What is a smart motorway?

5th September 2022
Sheryl Miles

The term ‘smart motorway’ isn’t a particularly new one. And seeing digital display screens attached to gantries above stretches of motorways – like the M3 and M25 – isn’t a new concept either. In fact, around 10% of the motorway network in the UK is already made up of smart motorways.

But what exactly are smart motorways?

Broadly speaking, they are a way of using technology to monitor and then respond to varying traffic fluctuations. They are designed to mitigate congestion and the costs associated with it, whilst maintaining the safety of motorists.

However, there is more than one smart motorway. There are, in fact, three.

The three smart motorways:

All-lane running (ALR)

This is where there is no hard shoulder. Instead, the traffic uses all the lanes, and there are emergency refuge areas (ERAs), or SOS lay-bys, spaced a maximum of 1.5 miles away from each other.


This has a permanent hard shoulder and implements the use of technology to set variable speed limits to control the flow of traffic.


This is where the hard shoulder is open at peak times, so it can be used as an extra lane to help traffic flow. You can only drive in this lane if it is open for traffic.

So, now we know what the different types of smart motorways are, the next question is, how do they work?

The technology

Sensors monitor speed flow, and smart motorways systems automatically respond by changing the speed limit by using:

Radar vehicle detection

Stopped vehicle detection is currently being rolled out and uses radar to detect individual stopped vehicles. The system then alerts control teams, who respond to the situation – whether that is by alerting the authorities or calling traffic officers to the scene.


A Motorway Incident Detection and Automatic Signalling (MIDAS) system monitors traffic and recognises the difference between queuing traffic or congestion using algorithms which allow it to recognise if mandatory speed limits need to be set, by displaying the appropriate signs on gantries above the motorway. It uses sensors to monitor the traffic flow and automatically turns on signs and signals when the motorway becomes busier.

Closed Circuit Television

Closed Circuit Television (CCTV) is also used to monitor the flow of traffic, and it works by liaising with the Regional Control Centre who will implement any responses to traffic flow, if needed.

The reason for the introduction of smart motorways is to keep the traffic flowing, mitigate queues and increase motorist safety. And it seems that, in theory, these motorways should work. However, the ALR system has raised concerns, with some believing that they are responsible for road-side deaths.

Newly elected prime minister Liz Truss has stated that she would “stop them if they are not working.” The government have also confirmed that they are not convinced it works, and are planning on pausing the system until five-years’ worth of data is available.

And it isn’t just the PM who has voiced her concerns over its safety. Members of the public have also cited that they do not feel ALRs are safe, and they have not been thought-out enough before being rolled-out to the public.

Questions have been raised over what happens if, for example, a car breaks down, then drives the 1.5 miles to its nearest EMA, only to discover that it is already occupied.

Or, what if it manages to navigate through lanes of traffic and parks in an EMA, but there is a disabled person onboard and they cannot get to safety – with the advice being to exit the vehicle on the left-hand passenger side, and shield from the road on the other side of the barriers when parked in an EMA.

One such thought could be to add the nearest EMAs to satnav and map devices, so if a person does run into difficulties, they have a good understanding of where their next refuge point is and what to do when they get there.

In theory the motorways should be a good idea, however, they still have some way to go before they really become smart.

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