Highways England's chief executive Jim O'Sullivan has told MPs that lives would have been saved if stopped vehicle detection had been in place on every smart motorway and all lane running schemes from the start.
Up in front of the Transport Select Committee at a time of great public concern about smart motorways, the session was always likely to put Highways England under pressure, despite Highways England's assurances that the schemes are as safe or safer than traditional motorways.
Mr O'Sullivan was joined by other Highways England top officials, Elliot Shaw, executive director of strategy and planning and Mike Wilson, chief highways engineer.
The key issue was SVD, as it is only in place across 18% of the smart motorway network and means that drivers breaking down in a live lane could spend much longer there before receiving help - in some cases over 15 minutes.
Mr O'Sullivan was asked directly by the chair Lillian Greenwood: 'If stopped vehicle detection had been in place on all lane running schemes from the start how many deaths would have been prevented?'
He replied: 'A number of them. It's impossible to quantify. A number of these accidents happened very quickly, I think one was 17 seconds, of the eight fatalities undoubtedly one or two might have been avoided but not all of them would.
'Stopped vehicle detection itself, because of the nature of the system, is only about 80 to 90% effective.'
When asked to explain why the technology had not been used from the start, Mr O'Sullivan seemed to duck the question but said it would be from now on.
The chair pressured both Mr O'Sullivan and Mr Wilson on the issue of stopped vehicle detection on smart motorways, particularly as the transport select committee had raised concerns in 2016 on the issue.
Mr Wilson had assured the committee in 2016 that it would be part of the standard roll out of smart motorways going forward and be retrofitted to existing schemes.
Ms Greenwood questioned why it was taking so long.
Mr O'Sullivan said: 'We are trailblazing the use of it This is groundbreaking technology. We had to prove it before we could roll it out. We are rolling this out as quickly as we can it's not just the technology is the complete case we have to be satisfied with the results in m25. You can't roll out something this complex on a prototype basis.
'We are currently developing plans for this. It has to be 'productionised'. There are a number of challenges but now we know it works - we have three years' experience on the M25 - our first retrofit for stopped vehicle detection will be on the M3 and we are doing that this year.
'We are productionising it so we can roll it out over 100s of miles it is quite a challenge. It will be incorporated in all schemes after 2020.
'Retrofit has a number rod challenges. Firstly, the equipment: he how does the new equipment fit with the old? It has to fit physically and it has to fit electronically.
'We also have to make sure the radio signals don't conflict. Most importantly you have to know the traffic management plan for extensive lane closures. We have to understand how we do the retrofit before we roll out the full plan but our intention is ultimately to do it for all these.'
He also revealed the government-owned company only has one supplier 'so there is a difficulty in scaling up'.
When asked why they didn't use the German system common on autobahns, Mr Wilson said the primary technology came from Sweden and had been used in tunnels.
He did not have the reasons to hand why the German system would not have been suitable but, Mr O'Sullivan argued it would have been looked and rejected.
The committee lost some patience with the officials over a lack of statistics. They were unable to provide comparative data between the different smart motorway systems, but argued that while they held the data and would send it on it was likely to be so small they would not have looked into it in detail.
Mr O'Sullivan did make the admission that ' with the wisdom of hindsight I would like them all to have been the same'.
In a competent performance under intense pressure, Mr O'Sullivan also revealed that Highways England planned to withdraw the use of a dynamic hard shoulder - where the hard shoulder goes in and out of use - on smart motorways.
He described the system as just too complicated and outlined how it was easy for the public to be caught out and find themselves driving in a closed lane.