Extra traffic from Transmission Gully will make congestion on State Highway 2 unbearable now that two other roading projects are on hold, says Upper Hutt mayor Wayne Guppy.
The long-awaited highway is due to be completed next year, and Mr Guppy says the shelving of two other roading projects in the Hutt Valley is bad timing.
The Petone-Grenada road, that would have linked northern Wellington to the Hutt Valley, and work on the Melling interchange on State Highway 2 would have eased traffic woes but are both on hold until 2028.
Mr Guppy said the extra traffic coming off Transmission Gully would make things worse.
"We've been waiting for Transmission Gully for 60 years ... and we're not going to get the maximum benefit out of it because the other projects have all been told no, gotta wait another 10 or 20 years or not at all."
He said the Melling interchange was already a chokepoint for traffic and that affected not just Hutt residents.
"You know how fluid everyone is in the Wellington region, whether you live in the city or in Upper or Lower Hutt, Porirua - even Wairarapa - and to have that deferred is really quite catastrophic for the Wellington roading network.
"Particularly economically, for people moving in and around the area, it's going to be a big issue for all of us."
Mr Guppy said he would continue to lobby government to bring the roading changes forward.
"We don't need to wait one year or ten years because if you're commuting on that road now there's issues already - morning and night there are issues - and not just in peak time. The projects just can't sit idly waiting for years to come."
A New Zealand Transport Agency spokesperson said its data showed the impact of Transmission Gully on SH2 would be minimal but that it had commissioned a further study which would come out prior to the motorway opening.