Party political games must not wreck plans for a new M4 relief road south of Newport, a Labour MP has warned.
Talks have resumed on Monday between Labour and Plaid Cymru to break the deadlock on the first minister post.
Plaid has ruled out any deal with Labour if the party went ahead with its M4 plan, known as the black route.
But Newport West MP Paul Flynn said the blue route alternative, favoured by Plaid, would make the city "a traffic hell".
Welsh Labour's preferred option for the M4 relief road is a brand-new six lane motorway over the Gwent Levels that could cost £1.1bn and has attracted criticism from environmentalists.
Plaid Cymru, UKIP and others prefer an upgrade of existing roads around Newport, including the A48 Southern Distributor Road (SDR) which runs along the city's outskirts to the south.
Mr Flynn, who did not explicitly refer to the Senedd talks, continued: "Party political games must not wreck a solution that will bring traffic relief to two thirds of the Welsh economy and tourist trade and ease killer pollution."
The MP claimed the UK government would react to the rejection of the black route by cancelling the Welsh Government's permission to borrow money for the M4 project.
"The funding will largely disappear," he said.
Mr Flynn said the blue route scheme would bring back congestion that the city suffered before the opening of the Southern Distributor Road in 2004, and that its role to re-distribute traffic "east to west, north to south" would be destroyed.
He said this would make Newport "a traffic hell of gridlock and pollution".
Mr Flynn argued the blue route was "favoured by people from elsewhere in Wales who long to pick up the scraps if the black [route] solution, is dumped".
Plaid Cymru's transport spokesman Rhun ap Iorwerth said: "The UK Government must not hold the people of Wales to ransom for the price of a new stretch of motorway that we do not want. It should be up to the people of Wales, and the Welsh Government, to find the right solution."
What is the blue route?
Proposals for the so-called blue route emerged in 2013 when a paper from the Institute for Welsh Affairs suggested congestion on the M4 around Newport could be eased for almost a third of the cost.
The price for the scheme, which would involve upgrading the SDR and the former steelworks road, was put at £380m.
Prof Stuart Cole, who wrote the report for the IWA, said the then Welsh Government was over-estimating likely traffic demands.
Under the proposal the roads would be upgraded to a two-lane dual carriageway at motorway or expressway standard, widening to a three-lane motorway in future if needed.
It would run from junction 28 at Tredegar Park to junction 23a at Magor.
Prof Cole declined to respond to Mr Flynn's comments, but said: "We are not going to get the increase of traffic that would need the black route.
"The blue route would do the job to ease traffic around the Brynglas Tunnels."
Mr Flynn's comments came ahead of talks resuming between Labour and Plaid Cymru over the delay in electing a first minister following the 5 May election, which left Labour short of a majority.
Formal discussions began last Friday - the first between the parties since Carwyn Jones and Leanne Wood were tied 29-29 in a Senedd vote last Wednesday.
The parties had said they were "confident" they could break the deadlock.
It is currently unclear when the assembly will reconvene to nominate the first minister.