Northbound traffic is being diverted via the solid square diversion symbol on road signs:

Exit the M6 at J28
At M6 J28 / B5256 junction, turn right and follow the B5256 eastbound (Leyland Way) for 0.3 miles.
At the B5256 / A49 junction, turn left and follow the A49 northbound (Wigan Road) for 1.7 miles.
At the A49 / A6 junction, turn right and follow the A6 eastbound (Lostock Lane) for 0.3 miles.
At the A6 / M6 Junction 29 roundabout, take the first exit and follow the M65 westbound for 0.4 miles.

Follow Hollow Diamond Diversion Symbol from here:

At M65 Junction 1a / A6 roundabout, take the first exit and follow the A6 northbound (London Way) for 4.6 miles.
At the A6 / A59 junction, turn right and follow the A59 eastbound (New Hall Lane) for 2.1 miles.
At the A59 / M6 Junction 31 roundabout, take the first exit to rejoin the M6 northbound