Drivers in and around the Forest of Dean will have 12 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 three closures already in place are expected to carry on this week:

• A40, from 7pm July 17 to 7am July 30, slight delays (under 10 minutes): A40 Over to Lea used as a diversion route for Gloucestershire County Council closure of the A449 Preston Cross.

• A38, from 8pm January 8 to 6am August 3, 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.

• A38, from 9am July 22 to 6pm August 20, slight delays (under 10 minutes): M50 both directions M5 jct eight to A449 Travellers rest roundabout, Lane closures for maintenance works.

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

• A38, from 9.30pm July 29 to 6am July 31, moderate delays (10-30 minutes): M50 both directions, junction 1, entry and exit slip road closures for maintenance works, diversion via National Highways network.

• A38, from 9.30pm July 31 to 6am August 2, moderate delays (10-30 minutes): M50 both directions, junction 2, entry and exit slip road closures and lane closures for maintenance works, diversion via National Highways and Local authority network.

• M50, from 9pm August 1 to 6am August 2, slight delays (under 10 minutes): M50 westbound, junction 1 to junction 2, Lane closure for maintenance.

• M5, from 10pm August 1 to 6am August 2, slight delays (under 10 minutes): M5 southbound, junction 13 to 14, lane closure for barrier repairs.

• A449, from 9.30pm August 2 to 6am August 6, slight delays (under 10 minutes): M50 both directions, junction 3, entry and exit slip road and lane closures for maintenance works, diversion via National Highways and Local authority network.

• M50, from 9pm August 4 to 6am August 5, slight delays (under 10 minutes): M50 eastbound, junction 2 to junction 1, Lane closure for maintenance works.

• A40, from 8pm August 5 to 6am August 7, slight delays (under 10 minutes): A40 Birdwood traffic lights in place for Severn Trent Water works.

• A40, from 8pm August 6 to 6am August 21, moderate delays (10-30 minutes): M50 westbound, junction 1 to junction 4, carriageway closure and lane closures due to resurfacing works, diversion via National Highways and local authority networks.

• M5, from 9pm August 12 to 6am August 13, slight delays (under 10 minutes): M5 northbound, junction 12, exit and entry slips closed for survey works, diversion for northbound, exit slip, M5 northbound to junction 11 and return, diversion for northbound, entry slip, M5 southbound to junction 13 and return.

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