The process of widening a bottleneck on the main road between London and Hastings in East Sussex will officially begin later this year, a Kent MP said.
Greg Clark said he had received confirmation from transport secretary Lord Adonis that plans to dual part of the A21 would be published this year.
He said the move would also signal the start of the process to improve the A21 between Tonbridge and Pembury, in Kent.
Construction would begin in January 2012, the Tunbridge Wells MP added.
"The years of waiting endured by local people are nearly over," said Mr Clark.
"Almost 12 years after the government cancelled the scheme in 1997, we now have the Secretary of State's written intention that the work will at last get under way."
Lord Adonis had also said another stretch of single carriageway on the A21 in Kent between Kippings Cross and Lamberhurst could start as early as June 2012, Mr Clark revealed.
Much of the A21, which passes through Kent and Sussex, is single carriageway.
Five Kent and Sussex MPs have campaigned for improvements to the A21, saying the work was vital to coastal regeneration around Hastings.