A report by the Commons’ Transport Select Committee (TSC) said there is not enough safety and economic data to justify continuing with the project.
It described the Government’s decision in March 2020 that all future smart motorways would be all-lane-running versions – where the hard shoulder is used as a permanent live traffic lane – as “premature”.
Concerns have been raised following fatal incidents involving broken-down vehicles being hit from behind.
Demonstrators protesting against smart motorways marched with coffins to the Houses of Parliament on Monday.
The TSC urged ministers to “consider alternative options for enhancing capacity” on motorways.The committee’s 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.”
Controlled smart motorways – which only use the hard shoulder as a live traffic lane during peak periods – have the “lowest casualty rates” of all roads across motorways and major A roads in England, the report noted.
It called for the Department for Transport to “revisit the case” for installing them instead of all-lane running motorways.
Measures included in an 18-point action plan to improve smart motorway safety published in March 2020 – such as retrofitting technology to identify stopped vehicles – fail to “fully address the risks associated with the removal of the hard shoulder”, the MPs warned.
Relatives of those killed on smart motorways have called for the hard shoulder to be permanently reinstalled on the roads.
But the committee was “not convinced” that such a policy would boost safety.
It concluded: “The evidence suggests that doing so could put more drivers and passengers at risk of death and serious injury.
“The Government is right to focus on upgrading the safety of all-lane running motorways.”
The report recommended that emergency refuge areas are retrofitted to existing all-lane running motorways to make them 0.75 miles apart “where physically possible”, and a maximum of one mile apart.
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.”
Smart motorways were first introduced in England in 2014 as a cheaper way of increasing capacity compared with widening carriageways.
There are about 375 miles of smart motorway in England, including 235 miles without a hard shoulder.
An additional 300 miles are scheduled to be opened by 2025.