The construction of smart motorways should be paused until promised safety improvements have been delivered and there is more evidence to assess the risks, MPs have urged.

The cross-party transport select committee criticised as premature the decision by Grant Shapps in March 2020 to press ahead with the use of the controversial motorways in the face of mounting concern about their safety.

While the government has maintained that smart motorways are as safe as conventional ones, MPs said that at least five years of trial data covering all variants of smart motorway, which manage road speeds through electronic signs and do not have a hard shoulder, were needed.

The report said that the available evidence was “limited and volatile”, and urged greater powers for the Office of Rail and Road to block new road schemes until it was satisfied of their safety.

The scale of measures needed to effectively mitigate the risks from removing the hard shoulder on motorways had been underestimated, MPs said, and Highways England (the old name for National Highways) and the Department for Transport had failed to deliver promised safety upgrades.

More emergency refuge areas should be retrofitted to existing all-lane running smart motorways to be never more than one mile apart, and every 0.75 miles where possible. The highway code should also be updated with instructions to drivers to create corridors to allow emergency services to reach the scene of incidents, according to the MPs.

The report did not go as far some campaigners in calling for smart motorways to be scrapped, after a number of motorists who had broken down in a live lane and been hit by other vehicles were killed. However, it said that Shapps’ so-called “stock take” and 18-point plan last year would not go far enough in addressing the risks.

MPs also questioned Shapps’ decision to end by 2025 the use of “dynamic” all-lane running, where the hard shoulder is sometimes used as a live traffic lane. They suggested that with clear, consistent use such motorways would be preferable, as they could retain the hard shoulder in quieter times.

Committee chair Huw Merriman said as only 29 miles of all-lane running smart motorways had operated for over five years, it “feels too soon, and uncertain, to use this as an evidence base to remove the hard shoulder from swathes of our motorway network”.

He said the focus on upgrading safety by ministers was welcome, “but we’ve been here before. We’re not convinced that reinstating the hard shoulder on existing schemes is the answer, but the DfT must pause the rollout and take stock.”

The select committee in June 2016 called on the government to drop or pause the rollout of smart motorways, which have been seen as a comparatively cheap and easy way to increase capacity on the UK’s major road networks. A report then concluded that the trade-off in safety was an “unacceptable price to pay” for all-lane running.

Motoring organisations welcomed the latest report, which they said was pragmatic and endorsed their calls for measures to improve safety.

Labour said it confirmed that ministers had wrongly pressed ahead in the face of overwhelming warning evidence. Jim McMahon, shadow transport secretary, said: “We know smart motorways in their current form, coupled with inadequate safety systems, are not fit for purpose and are putting lives at risk. Reinstating the hard shoulder while full investigations are carried out need not be costly … the government must finally listen.”