The New Zealand Transport Agency (NZTA) has scrapped plans to build a four-lane expressway from Otaki to Levin in favour of upgrading the existing highway.
NZTA said the upgrade would cost under $100 million - about $300 million less than an expressway.
"We've looked at various options on different routes, and we've decided that progressively upgrading the existing State Highway 1 and SH57 routes is the best approach for this section of highway," said NZTA Wellington state highways manager Rod James.
"This will provide for early improvements to address current problems, while also providing for the staged development of a higher standard highway as demand increases over time."
Mr James said a detailed package of improvements would now be developed, ahead of further consultation with the community later in the year.
"There will be a strong safety focus to these proposals, aimed at making journeys safer for everyone. In particular, the improvements will be addressing problem areas that will be well known to regular drivers of this route, such as the forest lakes section, rail and river bridges at Manakau and Ohau, as well as some problem intersections and providing additional passing lanes and barriers."
An NZTA spokesman said cost was a factor in the change of plan. NZTA had not ruled out a four-lane expressway being built some time in the future.
The 30km section of SH1 from Otaki to Levin is part of the Wellington Northern Corridor, which has been identified by the Government as a road of national significance.
Horowhenua Mayor Brendon Duffy told Radio New Zealand the upgrade would just move the bottleneck from Otaki to Levin.
"Definitely there's going to be improvements and I absolutely acknowledge that there will be improvements much earlier, and hopefully that will give us the safety factor, but it doesn't remedy the major issue," he said.
"I still see Horowhenua in 50 years time as a satellite of Wellington and we need to have good access to it, not only for Horowhenua to get into the city but for city people to get out to this part of the world. It needs to be an ultimate goal."
He said increased traffic through Levin could be good for shopkeepers, "but I don't think it adds to the environment of a lovely retail strip - you've got SH1 charging straight through the middle of it".