The Forest of Dean's motorists will have 13 road closures to avoid nearby on the National Highways network this week.

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

The latest expected works list, with notes from National Highways, shows that one closure already in place is expected to carry on this week:

• A38, from 8pm January 8 to 6am July 31, severe delays (more than 30 minutes): M5 northbound and southbound, junction 7 to junction 11, 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.

And a further 12 closures will begin over the next two weeks:

• M4, from 8pm July 1 to 6am July 2, moderate delays (10-30 minutes): M48 eastbound, junction 2 to junction 1 Severn Bridge carriageway closure for structure maintenance, diversion via M4 Prince of Wales Bridge, diversion for, junction 1 via M4 J22, M49, A4 and A403.

• M48, from 8pm July 1 to 6am July 2, slight delays (under 10 minutes): M48 westbound, junction 1 to 2 Severn Bridge lane closure for structure maintenance works.

• A40, from 8pm July 1 to 6am July 3, slight delays (under 10 minutes): A40 Birdwood traffic lights in place for Severn Trent Water works.

• M48, from 10pm July 1 to 6am July 6, slight delays (under 10 minutes): M48 both directions mobile lane closure for drainage works.

• M48, from 8pm July 2 to 6am July 3, slight delays (under 10 minutes): M48 eastbound, junction 2 to 1 Severn Bridge - lane closure for structure maintenance.

• M4, from 8pm July 2 to 6am July 3, moderate delays (10-30 minutes): M48 westbound, junction 1 to 2 Severn Bridge carriageway closed for structure maintenance works, diversion via M4 Prince of Wales Bridge.

• M4, from 9pm July 3 to 6am July 5, moderate delays (10-30 minutes): M4 eastbound, junction 23 to 22 Prince of Wales Bridge closed for carriageway renewals, diversion via M48 eastbound to M4, junction 21.

• M4, from 9pm July 4 to 6am July 5, slight delays (under 10 minutes): M4 westbound, junction 22 to 23 Prince of Wales Bridge - lane closures for bridge maintenance.

• M4, from midday, July 5 to 1am July 10, moderate delays (10-30 minutes): M4, junction 21 to M48, junction 2 both directions plan your journey expecting increased traffic flow for music events at Chepstow race course.

• A449, from 9pm July 7 to 6am July 8, moderate delays (10-30 minutes): M50 eastbound, junction 2 to junction 4, carriageway closure for maintenance works, diversion via National Highways and Local authority network.

• A40, from 8pm July 8 to 6am July 13, slight delays (under 10 minutes): A40 both directions Lea to Huntley - two-way signals for inspection/surveys.

• M4, from 9pm July 8 to 6am July 13, slight delays (under 10 minutes): M4 eastbound, junction 23 to 22 Prince of Wales Bridge - lane closure for carriageway renewals.

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