A radar system that should alert the smart motorway control room to breakdowns within 20 seconds gives a host of false warnings – while missing stranded cars.
Stopped Vehicle Detection (SVD) has been lauded by highways chiefs and ministers as 'ground-breaking'.
But control room staff say the system – to be expanded along the entire smart motorway network at a cost of £122million – is impossible to rely on.
It currently 'protects' 24 miles on the M25 around London and 13 miles on the M23 in Surrey.
Staff view alerts from the system, which makes a 'groaning' sound when it is triggered, as 'low priority' because it goes off so often. Slow-moving traffic and even road signs set it off.
In a series of logs seen by the Mail, staff say it often misses breakdowns. Labour's transport spokesman Jim McMahon lambasted the tech, saying it 'isn't fit for purpose'. 'The Government is notorious for bad IT projects', he said. 'You can't have a bad IT project when people's lives are being put at risk.'
Former roads minister Sir Mike Penning said: 'Even one minute sitting in stranded traffic is unacceptable.'
Transport Secretary Grant Shapps ordered the technology to be installed across the network by March 2023 as part of an 18-point plan to improve safety.
The system works through radar posts spaced every 500metres along the motorway.
They are supposed to identify and locate stopped vehicles and then alert the control room.
Staff are then meant to use CCTV to pinpoint the location and check whether there is an accident or breakdown.
The M3 smart motorway near Camberley in Surrey. The motorways have no hard shoulder for emergencies, and use technology to close off lanes
Former transport minister Andrew Jones said in 2016 the system had been 'successfully trialled' and was an 'important measure... which we believe will help reduce the risk associated with stopping in live lanes.'
In 2019, former Highways England chief Jim O'Sullivan told MPs the system is 'ground-breaking technology' and trials on the M25 had 'proved that it works'.
Mr O'Sullivan, who said they had been 'perfecting the design of smart motorways for ten to 15 years', added: 'Getting it right and making sure it works in all geographies and topographies as we roll it out is very important to us.'
But – in marked contrast – internal reports reveal staff flagged system failures to highways bosses several times over the past few months.
On June 4 an operator warned there had been 48 false alarms in five hours at the same location.
On August 25, staff said the system had been 'suppressing itself' and a stranded car 'in lane one of four not picked up'. Another said the radar system 'constantly goes off, but nothing is ever there on CCTV. This has been a regular occurrence for over a month now. It needs to be fixed.'
A fourth said a contractor reported a broken-down vehicle on a smart motorway live lane 'with a recovery truck also stopped in lane one fending it off' but there was no SVD alert.
An undercover reporter working at the National Highways South Mimms control centre witnessed the system fail to detect a car sitting in speeding traffic on the M25 for more than 30 minutes. Luckily it had been spotted by staff.
A staff member, who has worked at the company for more than a decade, said: 'If that [SVD] works the way it should work, it's much safer…But he could be sat there for hours and we wouldn't even know about it, and if we don't know we haven't set signals.'
Transport Secretary Grant Shapps ordered the technology to be installed across the network by March 2023 as part of an 18-point plan to improve safety
He added: 'That's when a truck comes along and hits him and we go 'Oh well we didn't know he was there'. If nobody reports it and he gets killed and they go, 'Why wasn't it actioned?' 'Because it never flashed up'.'
One operator said: 'When they introduced the smart motorways, the justification
