Highways England chose 'cheapest and worst' A358 proposal
Highways England proposed the cheapest way to upgrade the A358 despite more costly options having more benefits, an investigation has found.
A local democracy campaigner obtained the Highways England documents using Freedom of Information (FoI) requests.
Campaigner Dave Orr said: "We now know it's been value engineered down because the budget is constrained."
Highways England says it will listen to all feedback from its current single option consultation for the upgrade.
"We've ended up with a scheme which delivers more problems with noise, pollution and disturbance, accidents than if we did nothing which I think is absurd," added Mr Orr.
In March, the government and Highways England put forward one option to dual the A358 between Southfields roundabout and Taunton in Somerset.
Since then councils have criticised the plans saying they lack detail and residents have complained that only one option was being consulted on.
The FoI documents show ideas which include linking the M5 to a planned new hi-tech business park at Henlade were ruled out, along with other proposals as they would cost between £366m and £451m.
According to the released documents, the single option was estimated to cost £366m but was "still in excess of the budget of £251m".
The report also stated: "We cannot commit to a Junction 25 link on affordability grounds."
A Highways England spokesman said: "The current scheme cost remains within the Road Investment Strategy allocation of £250m - £500m."
Taunton MP Rebecca Pow has raised the issues with the Secretary of State for Transport, Chris Grayling.
She said: "We need to look at why only route was offered because there was a feeling that initially more routes were going to be offered."
She added that the upgrade needed to bring "economic gain" to Taunton and link to the new business park, which is set to attract more than 4,000 jobs.
The consultation closes on 16 July.