Major work will be carried out to tackle notorious traffic bottlenecks on the main route through Cornwall.
The government has confirmed contributions to £180m plans to dual two stretches of the A30 over the next five years.
Cornwall's tourism chief said the schemes could bring in an extra £50m a year in tourism cash.
The traffic improvements form part of the government's five-year national Road Investment Strategy.
The government said work would start immediately on developing proposals for a £120m scheme on the 7.7-mile (12.5km) stretch of A30 between Carland Cross and Chiverton Cross.
Funding was also confirmed to use £60m to also make 3.1 miles (5km) of road over Bodmin Moor between Temple and Higher Carblake, a dual carriageway.
John Pollard, leader of Cornwall Council, said: "The completion of these much needed schemes will play a vital role in reducing delays on the A30 which currently costs over £10m a year in lost time alone.
"They will also play an important role in the future prosperity of Cornwall by encouraging economic growth, aiding regeneration and business expansion and supporting tourism."
Tourists 'put off'
Malcolm Bell, chief executive of Visit Cornwall, said the traffic jams "tested the loyalty" of holidaymakers.
He said: "Bearing in mind that our customers have to drive through our competitors, it can put people off."
Mr Bell said more than 85% of visitors to the county come by road.
He said: "The short-break market is retracting towards Bristol and we think that's because of traffic issues.
"If we get a 10% growth in the short-break market that would bring in an extra £50m a year."
The government also announced a scheme to construct a 1.8-mile (2.9km) tunnel at the A303 past Stonehenge.
The scheme is part of a £2bn plan to make the entire route - from London to the South West - a dual carriageway.