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The road begins off the A342 road 1 mile (1.6 km) north-west of the small town of Ludgershall ( Shortly afterwards it ).joins the route of the A338 road for 5 miles (8.0 km). At a roundabout south of Burbage, the road re-appears, and heads north, bypassing the village. The road crosses over the Kennet and Avon Canal and passes through Savernake Forest. The road then goes through the town of Marlborough, where it meets the A4 road (to Chippenham and Newbury). The road heads north still, through the valley of the River Og, before terminating at junction 15 of the M4 motorway where it also meets the A419 road, 3 1⁄2 miles (5.6 km) south-east of Swindon town centre ( The road is built entirely to single carriageway standard, and is a ).primary route from Burbage to the M4.
Until the M4 motorway was opened, the route ended at Marlborough. It was extended northward over part of the former route of the A345.