Critics have called for a new road crossing linking Kent and Essex to be halted after the government paused the roll out of smart motorways this week.
The Thames Crossing Action Group (TCAG) – opposed to the plans for the proposed Lower Thames Crossing – say continuing with the tunnel would be "building a smart motorway by stealth".
The group says it was told in an email by National Highways the road, which would cross from the A2 between Gravesend and the Medway Towns to link up with the M25 in Essex, would be "designed to smart motorway standards".
But in light of a decision this week pausing the construction of new smart motorways amid road safety fears, the group has now written to Grant Shapps, the transport secretary, urging a pause on the £8.2 billion Lower Thames Crossing project. Highways bosses say they are reviewing whether changes to the LTC design need to be made.
A critical report by a cross-party parliamentary committee said the features of a smart motorway – including no hard shoulder, lane detection and incident detection technology and vehicle emergency refuge areas – were more dangerous and therefore risked safety for drivers.
Laura Blake, chairman of TCAG, said: "National Highways is effectively building a Smart Motorway by stealth with its construction of the Lower Thames Crossing. It is notable that when we raised concerns about it being a smart motorway National Highways suddenly stopped calling it a motorway.
"They now refer to it as an all-purpose trunk road to try and hide what they really want to build.
"We’re calling on Grant Shapps to pause the Lower Thames Crossing. It’s a smart motorway in everything but name.
"We trust that he won’t be hoodwinked by National Highways’ renaming of the scheme. Now that we have raised this oversight with him, we trust he will be move to reassure the public at the earliest opportunity."
The group says it was sent information by National Highways which would see the 14-mile route have refuge areas 1.6km (one mile) apart and stopped vehicle technology to close lanes to traffic by detecting incidents and automatic signals on gangways above the road in line with government regulations.
The information also said the technology would be used to change lane signals if vehicles were identified to have stopped in the lane before one of the refuge areas.
But TCAG says it can see "no valid reason" for the crossing to be excluded by the pause given the previous admission it would be designed to the temporarily scrapped smart motorway principles.
The group added the scheme's risks are now even higher in a tunnel with no hard shoulder and few safety areas.
Mark Bottomley, development director for Lower Thames Crossing said: “Safety is our highest priority. The new crossing will be an all-purpose trunk road, similar to the A13 and other A-roads in Essex that are used by tens of thousands of people every day.
"It is being designed to the highest standards recommended today, but we will continue to adapt our plans to incorporate advances in safety design and technology that will come forward in the years ahead.
"While the crossing is designated as an A road we will of course be reviewing the Government’s announcement and considering any changes we may need to make."