The A12 at Darsham is shut 9pm to 6am on weeknights until 21 August for Sizewell C works, and Leiston's level crossing stays closed until 20 September.

The A12 at Darsham is closed on weeknights this week and next, from 9pm to 6am until Friday 21 August, while Sizewell C contractors build a new pedestrian crossing. The project’s latest works bulletin, published on 7 August, states: “The A12 at Darsham will be closed at weeknights (9pm-6am) from 10 to 21 August for works associated with a new pedestrian crossing.” (Sizewell C works tracker, traffic management bulletin, 7 August 2026)

The signed diversion is long in both directions: northbound traffic is sent via the A1120, B1116, B1117 and A144, and southbound traffic via the B1387, B1125 and B1122. Anyone driving between the Woodbridge area and Southwold or Halesworth late in the evening should allow extra time or travel before 9pm.

The same crossing works bring the A12 at Darsham back to weeknight closures later in the year, from 7 to 18 September and again from 5 to 16 October, at the slightly earlier hours of 8pm to 5am. (Sizewell C works tracker)

Leiston level crossing closed until 20 September

The closure at Leiston level crossing, in place since 27 July, has been extended. In an update published on 7 August the project said: “Unfortunately, we need to extend the current closure at Leiston level crossing on Station Road for up to a further three weeks”, adding that the closure “is now expected to remain in place until 20 September 2026”. The extra time is needed to protect a fragile utility pipe discovered during the works while it is replaced, and the approved diversion routes stay in place. (Sizewell C works tracker, Leiston level crossing update, 7 August 2026)

The weekly bulletin lists the same closure as the B1122: “From 27 July to 20 September, Abbey Road (B1122) will be closed 24/7 at the Leiston level crossing.” The level crossing on The Green at Knodishall is also shut, from 5 August to 5 September. (Sizewell C works tracker)

Timeline of Sizewell C road closures from August to October 2026: the B1122 at Leiston level crossing closed 24 hours a day from 27 July to 20 September, The Green at Knodishall closed 5 August to 5 September, the A12 at Darsham closed on weeknights 10 to 21 August, 7 to 18 September and 5 to 16 October, and the A12 at Marlesford closed at night from 19 September to 4 October
Graphic by Suffolk Coast News.

More on the way this autumn

The bulletin sets out a heavy programme for September and October. The A12 at Marlesford, south of the Darsham works, will be “closed at nights (8pm-5am) from 8pm 19 Sept to 5am Sunday 4 October”, with a diversion via the A1152, B1069 and A1094. There will also be “weekend closures of the B1122 throughout September, October and November”, with dates still to be confirmed.

Two long closures for the Sizewell Link Road also began on Monday 10 August: Fordley Road at Middleton cum Fordley is closed until the third quarter of 2027, diverting via Town Farm Lane, the A12 and B1122, and Hawthorn Road near Theberton is closed until 30 April 2027. (Sizewell C works tracker)

What it means for you

For most readers the immediate change is the A12 itself: until 21 August, any weeknight trip up the coast after 9pm means the full diversion loop, so time journeys to Southwold, Walberswick or Halesworth accordingly. Leiston residents face the level crossing closure for another five to six weeks on top of the two weeks already served, and the village’s diversion routes carry the extra traffic 24 hours a day, not just at night.

The autumn dates are worth putting in the diary now, especially the overlapping window in late September when the A12 at Marlesford is shut at night while the B1122 weekend closures run. Our roadworks and travel page keeps the running picture for the area, and the project publishes its bulletin weekly on the works tracker.