Work has begun on a £65m bypass for the village of Blunsdon near Swindon, seven months ahead of the scheduled start.
The scheme will provide the village with a two-mile dual carriageway bypass and a two-level junction replacing Turnpike roundabout.
The new route is designed to reduce congestion and improve safety, making journey times more reliable both on the trunk road and in Blunsdon.
The scheme is expected to open by the end of 2008.
Roads minister Dr Stephen Ladyman said: "I welcome the news that work is ready to start ahead of programme on this important road improvement for Blunsdon.
"The bypass will remove almost all the through-traffic from Blunsdon village, making it safer and quieter for the residents, and it will improve journey times for traffic on the trunk road."
Highways Agency project manager David Radway said: "In the first full year most of the work will be done away from the existing road, so there will be minimal disruption to our customers.
"Traffic management measures will be introduced on the A419 in the second year so that work at Turnpike roundabout can be completed safely."