Thirty-eight people have been killed on smart motorways in the last five years, the government has told BBC Panorama.
It is the first time that the total number of deaths has been reported.
Smart motorways have been criticised because they do not have a hard shoulder and drivers who break down can be trapped in the speeding traffic.
The network is facing an overhaul with the results of a government review due to be announced shortly.
A Freedom of Information (FoI) request sent by Panorama to Highways England revealed that on one section of the M25, outside London, the number of near misses had risen 20-fold since the hard shoulder was removed in April 2014.
In the five years before the road was converted into a smart motorway there were just 72 near misses. In the five years after, there were 1,485.
A “near miss” is counted every time there is an incident with “the potential to cause injury or ill health”.
The FoI request also revealed that one warning sign on the same stretch of the M25 had been out of action for 336 days.
The idea behind smart motorways was to improve the flow of traffic through the most congested parts of the network by using the hard shoulder as an extra lane.
There are currently 200 miles of smart motorway and another 300 miles are due to be converted by 2025.
There are around 90 deaths per year on the UK’s motorway network as a whole, which covers about 2,300 miles of road.
The figure of 38 deaths over five years on the smart motorway network is significant because it only makes up a small proportion of the total miles of road.
Transport Secretary Grant Shapps told BBC Panorama he wants to fix smart motorways because they are too confusing for drivers.
He said: “We absolutely have to have these as safe or safer than regular motorways or we shouldn’t have them at all.”
A government review, the results of which are due to be announced shortly, is expected to recommend reforms to improve safety.
Panorama understands that radar will be fitted across the whole smart motorway network over the next three years.
The car detection system – which is currently only fitted on two sections of the M25 – can spot stranded vehicles as soon as drivers break down.
Nationally, motorists currently have to wait an average of 17 minutes to be spotted, and a further 17 minutes before they are rescued.
The government is also planning to scrap so-called dynamic hard shoulders, which are sometimes used as a hard shoulder and sometimes used as a live lane for traffic.
The BBC understands there will also be more emergency lay-bys.
It is unlikely to satisfy road safety campaigners.
The former government minister who approved the roll-out of smart motorways told Panorama he was misled about the risks of taking away the hard shoulder.
Sir Mike Penning 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 the Conservative MP. “There are people that are being killed and seriously injured on these roads, and it should never have happened.”
An all-party group of MPs, led by Sir Mike, will publish a report on Monday that accuses Highways England of “a shocking degree of carelessness”.
The MPs say there should be no further roll-out of smart motorways until further research is conducted into their safety.
Highways England said the plans to expand smart motorways were approved by ministers and that it was working to gather the facts about safety.
A spokesperson said: “Any death on our roads is one too many, and our deepest sympathies remain with the family and friends of those who lost their lives.”
Eight-year-old Dev Naran was killed on a smart motorway when he was on his way home from visiting his critically ill brother in Birmingham Children’s Hospital.
His grandfather stopped the car on the inside lane of the M6 and the vehicle was hit by a lorry 45 seconds later.
Mum Meera Naran told the programme that after the accident Dev’s body was then taken back to the hospital where his brother was being treated.
“I had both my boys, one fighting for his life still and Dev just there. It wasn’t right, my two sons, one really sick, and the healthy one left me.”
AA president Edmund King said that taking away the hard shoulder had made breakdowns on the motorway more dangerous.
“It’s just the most awful situation when you’ve broken down and your kids are in the back of the car, and there’s nothing you can do to protect your kids.
“I certainly believe smart motorways are a scandal because, as we’ve been saying from the outset, they are dangerous, they’re not fit for purpose.”
Panorama, Britain’s Killer Motorways? is on BBC One at 20:30 GMT on Monday 27 January, or watch later on iPlayer