Drivers in and around the Forest of Dean will have seven National Highways road closures to watch out for this week.

And one of them is expected to cause major delays – with motorists facing a wait of at least 30 minutes. Another three will cause moderate delays of between 10 minutes and half an hour.

The latest expected works list, with notes from National Highways, shows that two closures already in place are expected to carry on this week:

• A38, from 8pm January 8 to 6am September 7, severe delays (more than 30 minutes): M5 northbound and southbound, junction 7 to junction 9, M50 eastbound, and westbound, junction 2 to M5, carriageway, slip road, lane closures, with 24/7 narrow lanes, lane closure, and 50mph speed limit due to improvement works, diversion via National Highways and local authority network.

• A449, from 9pm August 21 to 6am September 7, slight delays (under 10 minutes): M50 eastbound, junction 4 to junction 1, Lane closure for maintenance works.

And a further five closures will begin over the next two weeks:

• A40, from 7pm September 2 to 6am September 10, moderate delays (10-30 minutes): A40 Huntley multiway traffic lights in place for Gigaclear works. Includes diversion onto the A40 Huntley to Birdwood, for closure of Grange Court Lane.

• M48, from 10pm September 2 to 6am September 7, slight delays (under 10 minutes): M48 both directions mobile lane closure for drainage works.

• A40, from 8pm September 3 to 6am September 4, slight delays (under 10 minutes): A40 both directions Highnam Rbt to Over Rbt, lane closure for barrier works.

• M4, from 8.30pm September 3 to 6am September 7, moderate delays (10-30 minutes): M4 eastbound, junction 23 to 21 Prince of Wales Bridge closed for carriageway renewals, diversion via M48.

• M4, from 8.30pm September 3 to 6am September 8, moderate delays (10-30 minutes): M4 westbound, junction 21 to 23 Prince of Wales bridge inc, junction 22 entry slip road carriageway closure for carriageway renewals, diversion via M48 westbound, For M49 northbound, traffic via M4 eastbound to junction 20, M5 southbound, exit, junction 16, join M5 northbound, M4 westbound.

National Highways is responsible for maintaining motorways and major A-roads, so closures of smaller roads will not be included in their schedule.