But the controversial project has been plagued by delays and setbacks, causing frustration for thousands of motorists.
Now, National Highways has confirmed the efforts to complete the M27 will be finished in a matter of months.
Finishing touches to the M3 towards Winchester have been stood down. National Highways chiefs confirmed the move following a letter to construction firm Balfour Beatty, in which the organisation said it would be ‘temporarily postponing’ the planned start of the £140m project to replace the central reservation.
The decision followed a report by MPs on the Commons’ transport select committee, which demanded five years of safety data be collected about the smart motorways.
The new style of highways use technology and other measures to cut congestion, such as opening the hard shoulder.
But there have been concerns about their safety after fatal accidents involving stationary cars being hit from behind.
National Highways said stopped vehicle technology – which can identify a stopped vehicle within 20 seconds and alert traffic controllers – would help to boost safety.
The authority added the the work to upgrade the M27 between junctions 4 and 11 were ‘nearing completion’ and so were ‘not affected by’ the transport select committee’s report recommendations.
A spokesman added: ‘Stopped vehicle detection is currently being fitted and we expect the upgrade to be fully open spring 2022.
‘We are making good progress on upgrading the M27 and we are grateful for people's continued patience through our roadworks
‘We had been expecting to open the first sections of these upgrades to traffic in the summer 2021, but in line with the recommendations made by the secretary of state we made the decision to wait until we've installed stopped vehicle technology.’
A spokesman for the Department for Transport added: ‘We welcome the transport committee’s scrutiny and will now consider its recommendations in detail, providing a formal response in due course. This is a serious piece of work which we will engage with closely in the months ahead.’