Smart motorways were introduced with the aim of increasing capacity and easing congestion by using the hard shoulder as an extra lane.
But they have been criticised by the government minister who originally approved the roll-out in 2010.
Speaking to Panorama in January, Sir Mike Penning, who is no longer a minister, said he had been misled about the risks of taking away the hard shoulder.
The Conservative MP said he had agreed to the expansion in 2010 after a successful pilot on the M42 near Birmingham.
The pilot worked well because there were safe stopping points for motorists, called emergency safety refuges, on average
every 600 metres.
But when the scheme was expanded across the country, the safety refuges were placed further apart - on some sections, they are
2.5 miles apart.
"They are endangering people's lives," said Sir Mike. "There are people that are being killed and seriously injured on these roads, and it should never have happened."