What is a smart motorway?

Published: 10 July 2023

If you’ve driven on any of the UK’s motorways in the past decade or so, you may have noticed that large sections of some have been converted into so-called smart motorways. But what exactly is a smart motorway and how do you drive on one? Our guide explains.

The first thing to understand is that a ‘smart’ motorway is really just a section of a ‘regular’ motorway that’s been adapted with technology designed to  improve the flow of traffic, often by increasing the number of vehicles able to use it.

There are three main types of smart motorways:

• Controlled motorways. These have variable speed limits and feature overhead gantries that display the current legal top speed. The limit changes depending on the traffic conditions, in an effort to prevent traffic bunching up at busy times.

• Dynamic hard shoulder (DHS) motorways. These allow you to drive on the hard shoulder at certain times. Signs on overhead gantries display whether the hard shoulder is open to regular traffic.

• All-lane running (ALR) motorways. These stretches have an extra lane for traffic instead of a hard shoulder. However, signs on overhead gantries are used to close the lane if, for example, a vehicle is blocking it.

There are two main reasons for creating a smart motorway. First, by converting the hard shoulder to a driving lane, more traffic can flow  without the expense of physically widening the road. Second, they’re designed to allow better control of that flow, in theory reducing congestion. That’s why smart motorways are generally added in areas prone to traffic jams.

Electronic monitoring systems and CCTV cameras constantly ‘watch’ smart motorways: the information and images are sent in real time to a control centre. When congestion or an accident develops, the control centre staff can take action, depending on the situation and the type of smart motorway affected.

For example, in times of busy traffic, the speed limit might be adjusted. This works  by controlling the flow of traffic heading into the busiest areas, to reduce build-up and stop-start congestion and keep vehicles moving. The limits are shown on overhead gantries and are enforced by speed cameras. If a gantry doesn’t display a limit, then the national speed limit applies.

On a DHS motorway, the control centre might also open the hard shoulder to traffic to increase the number of usable lanes and make room for more vehicles. Gantry signs will advise whether the hard shoulder is open or closed.

 ALR motorways have all lanes open by default, which means there’s no hard shoulder to pull over if you have a problem. The solution is to pull into a lay-by type of space known as an emergency refuge area (ERA) and call for assistance using the special telephone each one has. An ERA is placed at least every 1.5 miles and is indicated by large blue signs and orange road surfaces. 

Sometimes the inside lane is closed on ALR motorways. This is done using signs on overhead gantries: you’ll  see a big red X above the closed lane, which means you need to move to another lane as soon as you safely can.

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It’s really easy to tell when you’re driving along a stretch of smart motorway. You’ll notice large overhead gantries every mile or so. Stretches of smart motorways also tend to have much more signage than you see on a regular motorway, so it’s important to stay alert and make sure you’re taking in all the information that’s being shown.

When you're driving on a smart motorway the overhead signs will tell you which lanes to use. The usual rules apply, though, so if you’re not overtaking, you should drive in whichever lane is farthest to the left.

The maximum speed limit on smart motorways is 70mph, the same as on regular motorways. However, depending on the conditions, the limit could be lower and could vary along a stretch of smart motorway to ease congestion or to slow traffic near an incident. Any change in the speed limit is shown on the overhead gantries as a number inside a circle. 

The limit shown on the gantry becomes the legal limit in force on that stretch of motorway: it’s not just advisory. Gantries are fitted with cameras monitoring the average speed of every vehicle. If a 50mph limit is in force for, say, three miles, the cameras can detect any vehicles exceeding the limit and penalty notices may be sent to those drivers.

Signs on overhead gantries on a smart motorway show if there are lanes closed ahead. You’ll first see that the speed limit has been reduced, then a mile or two later you’ll see arrows displayed on the gantries indicating that you need to safely move out of the lane that’s about to close. Another mile or two further along, you’ll see a red X displayed on the gantries above the closed lane.

Beyond that point, you must not drive in the closed lane. Doing so could put workers, other road users and yourself in danger. If you’re caught driving in a closed lane, you’ll receive three points on your driving licence and a £100 fine.

If you run into car trouble on a smart motorway, your next step  will depend on what kind of smart motorway you’re on.

If there’s a hard shoulder, then you should do the same as on any other motorway – pull onto it, put on your hazard warning lights and get everyone out of the car and behind the barrier (or away from the road if there’s no barrier). Then call the emergency services using a mobile phone or an SOS phone (located at regular intervals on the motorway). Signs will point you to the nearest one.

On an ALR motorway, you should try and get to an emergency refuge area. These ERAs are placed at regular, short intervals and indicated by signs with orange SOS messaging. Once parked, put on your hazard lights, get everyone out of the car and behind the crash barrier, and then use the SOS telephone to speak to someone at the control centre who will organise assistance.

If you can’t get to an ERA, move to the inside lane, and stop as far left as you can. If there’s no barrier, go as far onto the verge as possible. Turn on your warning lights and leave the vehicle (using the left-hand door if you can) and wait behind the safety barrier (if there is one).

Controversy has surrounded smart motorways ever since the concept was invented. Supporters say the technology provides extra capacity on roads and allows for better control of the traffic flow, reducing journey times. Critics say the lack of a permanent hard shoulder creates a safety hazard and they point towards a number of fatal accidents involving stationary vehicles.

In response to the debate, the government paused work on new stretches of smart motorway in 2022, and in April 2023 announced that no new smart motorways would be built, citing a lack of public confidence. All plans for future stretches were scrapped, including some that were already being built.

In the short term, no new smart motorways will be built following the government decision of April 2023. However, there are no current plans to reinstall hard shoulders on existing smart motorways. Instead, £900 million of previously planned work will continue as a way to improve safety via new ERAs and to upgrade the system that detects stopped vehicles and closes lanes.

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