Councillor Lezley Picton said that the full assessment of the costs of the controversial project would have to wait until the 'full business case' is produced – which can only be completed after planning permission has been approved.
There has been much speculation over the ultimate cost of the Shropshire Council project, which would complete the ring road around Shrewsbury.
The scheme was originally expected to cost around £81 million – with £54.4m coming from the Government, £28.5m from Shropshire Council, and £4.2m from the Marches LEP – although those costings date back to 2018, with inflation meaning the project will certainly be more expensive if it goes ahead.
Last October, Shrewsbury & Atcham's Conservative MP Daniel Kawczynski wrote to the Department of Transport asking for extra funding to cover the expected overspend – requesting £27.25m, which he said would cover 75 per cent of the increase in costs.
However, the Government has said no decision on extra money will be made until the full business case has been received.
The plans are finally expected to go before a planning committee in the coming weeks after the council responded to long-standing concerns from the Environment Agency and Natural England.
Councillor Picton said that only once the scheme has been approved will they be able to fully assess the final costs – and what may be required.
She said: "Until we get planning permission we cannot move to the full business case. At that point we can say to the Department for Transport 'Is there any possibility of further funding?'."
She added: "If and when we have planning permission we will move to the next stage."
Councillor Picton said there would be other sources of funding available apart from Westminster – but again said they would have to wait until the issue of planning permission has been settled.
The council leader has also said she remains personally committed to the project, adding that she believes it is essential to move traffic out of Shrewsbury's town centre.
"I have not changed my view. The North West Relief Road is required to continue that loop – it should have been built 40 years ago," she said.
"It is required to move traffic out of the town centre. That traffic is there now, we just need to be able to deal with it better."
Councillor Picton also said she believes a 'silent majority' are in favour of the road, but that people are reluctant to show their support in public.
She said: "When I was knocking on doors during the last election campaign the number of people who said 'If you don't build that road...'. They have been waiting years for that road."