North Yorkshire MPs have been urged to back a scheme to make the A64 a dual carriageway.
Campaigners have repeatedly called for the road, which links Leeds, York and Scarborough, to be widened to ease congestion.
National Highways have said proposals to dual a seven-mile stretch of the road north-east of York are “high cost but low value for money”, but the government is expected to make a final decision on the scheme next year.
At a full North Yorkshire Council meeting on Wednesday, councillors voted in favour of a motion urging the region’s mayor and the MPs for York Outer, Thirsk and Malton, and Scarborough and Whitby to confirm their support for “this essential upgrade”.
Councillor Keane Duncan, the Conservative-led authority’s former transport boss, told the meeting the project would not receive funding without “united backing”.
He said: “A vote for dualling today will not triumphantly end this 50-year struggle, but a vote against will no doubt doom hopes of dualling for good.
“We have a Labour government and while criticising them may feel tempting, it would not be fair, and it will not help.
“What will make a difference is cross-party pressure, with local Labour representatives playing a critical role in advocating for this upgrade with Labour ministers.”
The Labour mayor for York and North Yorkshire, David Skaith, suggested earlier this year that bus and rail improvements should be prioritised ahead of the dualling, which led to criticism from the Conservative MP for Thirsk and Malton, Kevin Hollinrake.
In response, York Outer MP Luke Charters said he was “always keen to support transport infrastructure that benefits my constituents in York Outer”.
Skaith, Hollinrake and Scarborough and Whitby MP Alison Hume have also been contacted by the BBC for comment.
