The RAC has called the government's plan to implement all-lane running on motorways and A-roads 'worrying'.
RAC chief engineer David Bizley made the comments after the government today defended the scheme in response to a report published by the Transport Select Committee in June.
The report slammed the plan to implement all-lane running across Britain's Strategic Road Network, which the government claims is needed to cope with a predicted traffic increase of up to 60 per cent by 2040.
The all-lane running system is a form of smart motorway, in which the hard shoulder is permanently converted into a running lane.
MPs on the committee said the 'dramatic change' to hundreds of miles of motorway and A-road would be dangerous.
In the official response to the committee's report released today, the government said that the evidence for all-lane running did not suggest safety concerns, claiming that instead it showed a "reduction in collision and casualty rates".
However, the RAC said it found the government's refusal to listen to the Transport Select Committee "worrying".
Bizley explained: "The safety case for all-lane running is not yet proven and as a result we fear that it won't be long before there is a major tragedy that will make the Government think again.
"Smart motorways are clearly part of the solution, but we have always said dynamic hard shoulder schemes, where the hard shoulder is only used as a running lane at busy times, provide the best compromise between increased capacity and keeping drivers, their passengers and roadside workers safe."
With the government going ahead with rolling out all-lane running, Bizley turned his focus to the proposed spacing of emergency refuse areas (ERAs), which are currently due to be placed at 1.85km intervals.
"An average ERA spacing of 1.85km apart substantially reduces motorists' chances of being able to reach one should they break down or be involved in an accident," he said.
"We believe ERAs should ideally be 800m apart and certainly no more than 1km apart."