The rollout of the M4 smart motorway could be halted after MPs raised concerns over safety.
A report by the Commons Transport Select Committee outlined the lack of safety and economic data to back the smart motorway project.
Protesters against these new motorway adjustments marched to the Houses of Parliament with coffins on Monday, November 1.
READ MORE:'Appalling' M4 smart motorway causing drivers to lose confidence
Smart motorways would see away with the hard shoulder, and instead, use that extra lane as a live traffic lane.
This has raised concerns over what would happen if there was a broken-down vehicle, with people worried about fatal incidents involving cars being hit from behind.
The Transport Select Committee has urged for other alternatives to be taken when trying to enhance motorway capacity.
The report said: "The government and National Highways should pause the rollout of new all-lane running schemes until five years of safety and economic data is available for every all-lane running scheme introduced before 2020 and the implementation of the safety improvements in the government’s action plan has been independently evaluated."
However, the report highlighted that smart motorways could be the solution if it was a 'controlled smart motorway'. These still have the permanent hard shoulder but use technology to regulate traffic and were found to have the "lowest casualty rates" of all major roads in England.
Those whose loved ones have been killed on smart motorways have called for the hard shoulder to be reinstated on all the roads. However, the committee doesn't think that is the right call either.
Tory MP Huw Merriman, who chairs the committee, said: "Looking at the available evidence, smart motorways do appear to be safer than conventional motorways even once the hard shoulder is removed.
"However, this evidence is also open to question. Only 29 miles of these all-lane running smart motorways have operated for over five years.
"It, therefore, feels too soon, and uncertain, to use this as an evidence base to remove the hard shoulder from swathes of our motorway network."
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A Department for Transport spokesperson said: "We welcome the Transport Committee’s scrutiny and will now consider its recommendations in detail, providing a formal response in due course. This is a serious piece of work which we will engage with closely in the months ahead.
"We’re pleased that the TSC recognises that reinstating the hard shoulder on all all-lane running motorways could put more drivers and passengers at risk of death and serious injury and that we’re right to focus on upgrading their safety, as the Secretary of State committed to doing when he became Transport Secretary."
Smart motorways were first implemented in 2014 in England and there are now roughly 375 miles of smart motorway in England whereby 235 are without a hard shoulder. An additional 300 miles are set to be instated by 2025.
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