Using the hard shoulder of motorways as an extra lane to ease traffic congestion could be dangerous for motorists, MPs have warned.
A Transport Committee report refused to endorse the concept while major safety concerns exist.
Chair of the committee, Labour MP Louise Ellman, said: “All kinds of drivers, including the emergency services, are genuinely concerned about the risk this presents.
“It is undeniable that we need to find ways of dealing with traffic growth on the strategic network.
“But All Lane Running does not appear to us to be the safe, incremental change the Department [for Transport] wants us to think it is.”
The hard shoulder is currently used as an emergency refuge area for vehicles on the motorway.
Plans to remove this over 300 miles of motorway is the latest version of a smart motorways scheme which uses active traffic management techniques to vary speed limits and the use of the hard shoulder in peak times.
Ellman added: “The government needs to demonstrate considerable improvement in this area, including more emergency refuge areas, driver education and enforcement, before the committee will endorse the extension of a scheme which risks putting motorists in harm's way.”
In 2015, the Department for Transport (DfT) forecasted that traffic on the strategic road network would increase by up to 60% by 2040.
The government sees smart motorways as a way of addressing this growth without incurring the costs of traditional motorway widening.
A DfT spokesman said: “Our motorways are among the safest in the world, and cutting the number of accidents is our top priority. All lane running roads are designed to be as safe as ordinary motorways.
“In the two all lane running sections on the M25, accidents were down 17% and casualty rates fell by 21% in the first year.”
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