Major construction work on the £88.6m managed motorway scheme on the M4 and M5 near Bristol is now underway.
Preparatory work - including site clearance and the installation of CCTV cameras started in November 2011.
Roads Minister Mike Penning officially started the main contract this week which will be complete in spring 2014.
The managed motorway scheme will cover 3.4 miles of the M4 between junctions 19 and 20 and 3.1 miles of the M5 between Junction 15 and Junction 17.
Penning said: "This start of work shows the Government delivering on its promise to invest in transport schemes that reduce congestion, improve safety, and support economic growth.
"The Highways Agency is ensuring value for money and making excellent progress against its commitment to reduce the cost of major capital projects by 20 per cent across the roads programme."
Work on the M4 and M5 will include strengthening the hard shoulder, building emergency refuge areas, installing gantries and electronic signs, and installing sensors in the road to measure traffic flow.
CCTV cameras will also be installed to monitor the motorway and emergency refuge areas.