Cornwall County Council is urging the government to come to a fast and positive decision on the inquiry into planned road improvements at Goss Moor.
If approved, the dualling would include the notorious Iron Bridge
Local residents and the business community, want to see a solution to the A30 bottleneck.
There are also calls for the single carriageway between Victoria and Indian Queens to be turned into a dual carriageway.
The inquiry was held in January, and the outcome is still awaited.
The possible dualling of the road at Goss Moor has caused controversy, as environmentalists say it is a special wildlife habitat.
County councillor Brian Higman, who lives at nearby Roche, said it was essential a decision was made soon.
"It's having quite an impact on businesses that we might attract into the county.
"It is also having an effect on businesses that are trying to decide whether they should expand or even stay in the county, and on the tourist industry."
He added: "It's the speculation that's causing the problem now.
"If somebody would come up with a straight 'yes' or 'no' answer we would know if we have to keep campaigning."
Debbie Smith, head of marketing at Cornwall Enterprise, said the road at present was an embarrassment for the whole county.
"In some ways perhaps it wouldn't be so bad if this was one of a number of routes into Cornwall, but this is our major route in," she said.
"If people's first impression of major access into Cornwall is of a small road that's congested, that has low bridges on it and piles of traffic ahead, it just doesn't set the right tone and show Cornwall in a good light."