Smart motorways have led to safety concerns, but highways bosses insist they are an effective way of boosting capacity.
Here the PA news agency answers 12 key questions about the roads.
– What is a smart motorway?
Smart motorways involve various methods to manage the flow of traffic, including variable speed limits and using the hard shoulder as a live running lane.
– How many are there?
Motorways with sections where the hard shoulder has been removed include the M1, M4, M5, M6, M25 and M62.
The RAC says the smart motorway network will cover around 500 miles this year, with an additional 300 miles planned by 2025.
Projects under construction include the M4 between Junctions 3 and 12, and the M1 between Junctions 13 and 16.
– What are the benefits?
They are designed to increase capacity without the more disruptive and costly process of widening carriageways.
– Are smart motorways safe?
Concerns have been raised about incidents where vehicles stopped in traffic are hit from behind.
But Highways England insists they are “at least as safe as, or safer than, the conventional motorways they replaced”.
– What does the data show?
An “evidence stocktake” published by Transport Secretary Grant Shapps in March stated that the risk of a collision between moving vehicles is lower on smart motorways than conventional motorways, but the chance of a crash involving a moving vehicle and a stationary vehicle is higher when the hard shoulder is removed.
BBC Panorama found that at least 38 people have died on stretches of smart motorways in the past five years.
– What was the result of this report?
An 18-point action plan included installing more places to stop in an emergency and faster roll-out of a radar-based system to detect broken-down vehicles.
– What happens if I break down on a smart motorway without a hard shoulder?
Drivers are advised to pull into an emergency refuge area (ERA) if possible.
– How frequent are they?
They were initially up to 2.5km (1.6 miles) apart, but for smart motorways designed from this year, they are no more than 1.6km (one mile) apart.
– What if I can’t reach an ERA or leave my vehicle safely?
If you come to a standstill in a live lane, call 999, switch on your hazard warning lights and stay in your vehicle with your seat belt on.
– What happens next?
Once Highways England is alerted to a stopped vehicle in a live lane, overhead gantries will display a red X to indicate the lane is closed.
– Are smart motorways used in other European countries?
The vast majority of motorway-style roads in Europe have a permanent emergency lane.
– What do drivers think about them?
An AA poll of 15,000 motorists suggested only one in 10 drivers feel safer on smart motorways without a hard shoulder than traditional motorways.