The Tories last night scrapped all new smart motorways after years of criticism.
Rishi Sunak wielded the axe after campaigners blamed the traffic schemes for up to 79 deaths.
Campaigners welcomed the move - but called for him to go further, extending the ban to all existing smart motorways.
Some 14 smart stretches which were in the works have been dumped.
The climbdown comes after repeated refusals to stop expanding the network even as fatalities continued.
The move follows years of campaigning by families of victims, inclding Clare Mercer whose husband Jason perished on the M1 in 2019 after new measures were implemented.
A minor accident turned to a double tragedy when a lorry hit Jason and fellow motorist Alexandru Murgeanu, apparently as they were exchanging insurance details.
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Coroner David Urpeth blamed their deaths on the smart system.
Mrs Mercer welcomed the news, but called on Mr Sunak to go further and scrap all existing smart motorways too.
"To have it confirmed that the ones in progress already are being cancelled is good news," she told the Mirror.
"I'm happy with the news this evening, but that's only half the battle."
She was dismayed to see that existing smart motorways would remain in operation, with 150 additional "emergency areas" installed across the network.
"A hard shoulder on every single motorway, that's the only thing I'll accept," she said.
"If they're saying the concerns are safety, how can they say the existing ones are OK to carry on?"
Around 10% of England's motorway network is made up of smart roads.
The system involve various methods to manage the flow of traffic, such as converting the hard shoulder into a live running lane and variable speed limits.
But there have been long-standing safety fears following fatal incidents in which vehicles stopped in live lanes without a hard shoulder were hit from behind.
“All drivers deserve to have confidence in the roads,” Mr Sunak said.
“Many people across the country rely on driving to get to work, to take their children to school and go about their daily lives and I want them to be able to do so with full confidence that the roads they drive on are safe.”
Labour MP Sarah Champion, who has campaigned in Parliament for Smart Motorways to be scrapped, said: "I’m relieved the Government has finally listened to motorists and common sense, but this announcement is long overdue.
"As ever with this Government, the devil's in the detail. Will they be returning the hard shoulder on existing conversions?
"Will the schemes currently in construction be restored?
"But above all, why now when 2 parliamentary select committee inquiries, their own review and countless campaigns by family members of those who died on these death traps wasn’t enough to persuade them?"
The Department for Transport said the construction of the scrapped schemes would have cost more than £1 billion.
But officials added the construction of two stretches of smart motorway at junctions six to eight of the M56 and 21a to 26 of the M6 will continue as they are already more than three quarters complete.
Existing stretches will remain but be subjected to a safety refit so there are 150 more emergency stopping places across the network.
