Motorists using will face lane closures, speed restrictions, and full closures overnight on stretches of both Severn Bridges while the work is carried out to remove the toll booths.
Highways England will oversee the work, which is expected to begin on or after Saturday December 1. It should be completed by mid-April next year.
According to a public notice published by Highways England, the traffic orders governing the work will enable the following restrictions:
M4: Overnight closure (8pm-6am), when necessary, of the M4 westbound, from junction 20 (M5) to junction 22 (M49), along with associated slip roads;
Overnight closure, when necessary, of the M4 Prince of Wales Bridge from 740 metres east of the bridge over the railway near Severn Tunnel Junction to a point just east of the westbound entry slip road at junction 22 (M49);
A temporary and mandatory 50mph speed limit on the M4 eastbound and westbound, from 740 metres east of the bridge over the railway near Severn Tunnel Junction to the western end of the Prince of Wales Bridge;
M48: Overnight closure, when necessary, of the M48 westbound from junction 21 of the M4 to junction one of the M48, along with associated slip roads;
Overnight closure, when necessary, of the eastbound and westbound carriageways of the M4 from 239 metres west of the westbound entry slip road at junction one to just west of the western end of the Severn Bridge;
Temporary and mandatory 50mph speed limits – on the M4 westbound from the Ingst Road Bridge to west of the entry and exit slip roads at junction one of the M48, and from junction one of the M48 to the eastern end of the Severn Bridge.
Width restrictions will also be imposed on vehicles of more than 2.5 metres wide on sections of the M4 and M48 around the toll booths.
Vehicles wider than 3.25 metres will be prohibited from using westbound sections of the M48 around the toll booths.
Lane closures will operate, and a hard shoulder will run, on both motorways throughout the works.
Diversions will operate via local roads when closures are in place. The Severn Bridge will be open westbound when the Prince of Wales Bridge is closed westbound, and vice versa.
The restrictions will not apply to emergency services or special forces vehicles.
For information on the Severn Crossings visit www.severnbridge.co.uk