The cost of the Heysham M6 Link Road has increased by more than £16m, according to a review of Lancashire County Council figures.
A review of the council’s statement of accounts for the past three years appears to show that it is expecting an over-run of at least £16.6m.
Lancaster City Coun Tim Hamilton-Cox said the initial £123.5m budget increased to £130m in 2014, and council officers are expecting the cost to rise again to at least £146.5m.
He said: “County officers need to explain why the cost over-run is happening and exactly what the final tab is going to be with only a few months left before the road opens.
“We also need to know how the contract with Costain is structured such that the taxpayer is picking up the cost of the over-run.
“According to a report by officers to County’s cabinet last month that over-run is £6.5m so far, but expected to increase further.
“However, a review of County’s statements of accounts for the past three years appear to show that County is already expecting an over-run of at least £16.6m, adding together actual and contracted spend on the project.
“At a time when libraries, children’s centres, the women’s refuge, the hostel for the homeless, and many more vital services in the district, are facing curtailment or closure because of County funding cuts, the link road cost over-run is not simply unacceptable - it’s a calamity.”
The link road, named recently as The Bay Gateway, is in the final phase of work and is expected to open in October.
The new bridge over the river Lune is already open to traffic, and work is continuing at various points along the road’s 4.8km length.
Lancashire County Council confirmed the cost of the road had over-run.
A statement is expected later.