Construction of the new junction will provide a connection into the Avonmouth and Severnside Enterprise Area from the motorway network.
The junction, which comprises two bridges, is also expected to promote local economic growth and reduce the number of lorries on the local road network.
Initial preparatory work on the scheme began in December 2017 ahead of main construction now starting.
Highways England is working with South Gloucestershire Council, Bristol City Council and the West of England Local Enterprise Partnership on the scheme, which involves using the existing bridge at Farm Lane with a second bridge being built immediately next to it.
Located to the south of the Western Approach Distribution Park and west of the village of Easter Compton, the two bridges will be incorporated into a single roundabout spanning the motorway with new access and exit slip roads connecting fully with both northbound and southbound traffic.
Two stubs will be left on the new roundabout when the scheme is complete. These will allow the junction to be connected to the local road network to support future development in this area.
Duncan Elliott, managing director of Galliford Try’s highways business, said: “We’re delighted to get cracking on a much-needed scheme that will bring far-reaching benefits. We have considerable experience of motorway work from our participation in the Smart motorways programme and will bring this to bear on the Avonmouth junction scheme.”
Completion is expected by December 2019.