Carillion will start work next month on widening a stretch of the A23 in Sussex to three lanes in each direction.
The £77m Handcross and Warninglid widening project is one of 14 major improvement schemes, worth £1.4bn, that the Highways Agency will start work on before 2015 subject to statutory processes.
Carillion’s A23 project team, which won the early contractor involvement contract seven years ago, are already on course to save £18m against previous estimates for the 2.4-mile widening job.
Roads Minister Mike Penning said: “Despite these tough times, the Government is investing in transport infrastructure to help the economy grow, while successfully to delivering more for less.
“The improvements being made here will tackle congestion that affects drivers on the A23 every day.
“The savings the Highways Agency has negotiated means the scheme will deliver an estimated £8 worth of benefits for the UK for every £1 we’re investing.”
Advance environmental work has been underway on the site since April 2011 and last October site clearance and tree felling began.
Main civil engineering work will start on 2 July and will involve narrow lanes and a temporary 40mph speed limit on the A23 between the Handcross and Warninglid junctions.