New bridge beams, that will eventually hold a wider roundabout, are being lifted into place over the weekend, which has resulted in the closure of the motorway at the Walsall and Wolverhampton junction until 6am on Monday (August 9).
Traffic is being diverted up the exit slip road, across the existing roundabout, and back down the entry slip road on the other side to rejoin the motorway.
Highways England has warned motorists of severe disruption to journeys in the days leading up to the work, and that's exactly what has happened, with hour-long delays reported by 6am on Saturday.
By 1pm those delays had reached 90 minutes, and at 3pm Highways England was reporting delays of up to two hours.
Tweeting just after 3pm the agency said there were over six miles of congestion northbound and queues of five miles heading south, and those queues remained at 5pm.
Expected to add 120 mins to usual travel times," the agency said.
The agency's map showed congestion on other roads in Wolverhampton and Walsall, while the M6 Toll tweeted to urge motorists to have their contactless cards ready to get through the booths quicker as a result of higher demand than usual, with motorists eager to avoid the M6.
Traffic will also be stopped entirely on occasions during the weekend when one of the four new beams - each weighing between 90 and 120 tonnes - is lifted into place. The first of those moments was at 8.30am on Saturday, with the second due on Saturday afternoon.
On Friday Highways England released a video of the 750-tonne crane - one of only four in the country strong enough to lift the beams - heading along the M6 to Junction 10 in a convoy with other lorries.
Motorists have been urged to avoid the area. One suggested route is to leave the M6 at nearby Junction 9 for Wednesbury, or Junction 11 if heading southbound.
From Junction 11, drivers can use the A462, the B4210 and the A35 Green Lane to reach Walsall, before using the ring road and following signs for the M6 to rejoin at Junction 9. Northbound drivers can use the same route in reverse to rejoin at Junction 11.
Thousands of motorists use the junction every day. Traffic regularly backs up on the Black Country Route and Wolverhampton Road at peak times and transport chiefs say the major project will help solve some of the issues faced by drivers. Work began at the junction at the start of the year.
The project, which is costing £78 million, involves replacing the 50-year-old bridges replaced with wider versions that will carry four lanes of traffic rather than the current two, a move which should ease congestion.
The beams for the south bridge will be lifted into place later in the year and will also require the M6 to be closed. The old bridges will be demolished later.
Highways England expects work on the new junction to be finished in 2022.