Pembrokeshire council wanted to build a dual carriageway on the A40
Plans to turn the A40 in west Wales into a dual carriageway have been scrapped.
A Welsh assembly committee has decided to abandon proposals to build two lanes each way which were put forward by Pembrokeshire council.
Instead, it has given the go-ahead to a series of minor upgrades which include a new by-pass around the village of Robeston Wathen, near Narbeth.
Pembrokeshire council said it was "at a loss" over the refusal of its plans.
The special assembly procedure committee's findings were published in a report which recommended a single carriageway over the local council's dual carriageway proposal.
It said the council's four-lane road plans did not represent better value of money than its own preferred three-lane option.
It also added its own option compared to the council's proposals avoided spending a "very significant amount of public money" to provide a standard of road which would not be justified on capacity grounds for at least 30 years.
Committee chair Christine Chapman said: "In reaching its decision, the committee had to consider on the basis of all the evidence it has heard, if the proposed scheme satisfies the test of being expedient and in the public interest.
"The committee finds that it does."
However, from the outset Pembrokeshire council petitioned that local public and business interests demanded that the A40 improvements should take the form a four-lane highway.
Council deputy leader and cabinet member for highways and planning Jamie Adams said: "We are at a loss to understand the conclusions of the report.
"The A40 is a major European network road which is the link between south Wales and southern Ireland.
"Our expert advice is that stretches of this proposed new three-lane road will be operating at over-capacity within two to three years of the completion date.
"The businesses which operate in Pembrokeshire - including ferry and freight companies and the energy firms around the haven waterway - together with tourist operators and the people of Pembrokeshire all rely on this route and overwhelmingly support our call for dualling."
Gordon James of Friends of the Earth said: "The dual carriageway on the A40 would increase traffic levels, increase the emission of greenhouse gases, it would be harmful for the environment, it would be hugely expensive.
"That money would be better spent on improving public transport, on health, on education, there's no need for it.
"We think the assembly committee has come to the right decision."