The North Devon Link Road could get a £250 million upgrade.
Devon County Council says it will help economic growth and improve safety.
Most of the investment will be to the northern end of the road, between South Molton and Bideford.
The road, which will be 30 years' old in 2018, was controversial from the start because of frequent switches between two lanes and one lane in each direction - thought to be the cause of many accidents.
The multi million pound cost could be spent in phases. The council's launching a consultation next week, but says it has no plans to improve the road between Tiverton and South Molton.
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