Removing the hard shoulder was a “lethal” cost-cutting decision which leaves motorists to fend for themselves if they break down on a smart motorway, MPs were told on Wednesday.

Sarah Simpson, a transport expert at engineering consultancy Royal Haskoning DHV, told the transport committee the “risks to life and limb” on all lane running motorways were “intolerable” to many motorists.

Explaining how she had studied 20 years of official documents before producing an independent report for the relatives of a man killed on the M1, she concluded the removal of the hard shoulder increased road capacity while still allowing for a “cost saving”.

She said one review found that because smart motorways were “very safe” there was an “opportunity to specifically design them to be less safe in order to save costs”.

Ms Simpson quoted the latest government statistics showing that in 2019, there were 25,500 live lane breakdowns on 1,500 miles of traditional motorway, compared to nearly 13,000 on just 200 miles of smart motorways, equivalent to 16 such breakdowns per mile per year on traditional motorways and 62 on smart motorways.

She said the removal of the hard shoulder “imposed a new hazard” with motorists failing to find a “safe refuge”, a problem still not resolved by a sensor system “that doesn’t work in the way envisaged” and a radar detection system which does not spot all broken down cars.

“The only mitigation is to rely on unreliable technology and the braking lights of vehicles following that broken-down vehicle,” she continued. 

“The real world implications are that drivers are stranded in live lanes effectively left on their own to navigate that situation.”

What to do if you break down on a smart motorway

She said the combination of these factors “was particularly lethal” and would not be allowed in similar industries, such as construction.

Greg Smith, a committee member, predicted a “total change” in the threat when electric cars become commonplace.

“There could probably be more breakdowns as people run out of electricity, particularly as batteries degrade.”

Ms Simpson said there was a “pressing concern” that autonomous cars are programmed only to brake – not swerve – when encountering a stationary car, which could make the dangers “considerably worse”. 

However, Kate Carpenter, a civil engineer specialising in smart motorway safety and fellow of the Chartered Institution of Highways Transportation, said despite it appearing “counter intuitive” smart motorways were safer and “the case was made” for them but they needed to be constantly monitored.

She warned that if drivers were “anxious” about smart motorways and shunned them they risked far greater dangers on A roads, which have a higher fatality rate.

She added how gantries relaying speed limits meant drivers were more attentive and so there were fewer lane changes and shunts in moving traffic on smart motorways.

A Department for Transport spokesperson said: “It is totally misleading to suggest that smart motorways were specifically designed to be less safe in order to save money.

“Smart motorways are designed to be at least as safe, if not more so, than the roads they replaced. In terms of fatality rate, they are the safest roads in the country.

“We recently committed to a raft of measures to further boost safety, including ensuring every new all lane running motorway opens with technology in place to spot stopped vehicles.”