The road begins at
County Gates in
Westbourne, before heading northward as a
grade separated dual carriageway, one of the main roads in the
South East Dorset conurbation. From near
Bournemouth International Airport it follows the western side of the
Avon valley,
joining the route of the
A31 road heading north-east for to cross the valley, before turning left at
Ringwood in
Hampshire where it joins the original,
single carriageway route to the east of the river. Heading northward up the east side of the Avon, it crosses to the west again near the town of
Fordingbridge. After crossing into
Wiltshire near
Downton, it meets the
A354 road at a roundabout near
Britford on the southern outskirts of
Salisbury, before joining the route of the
A36 road as it bypasses the city centre to dual carriageway standard. It then joins the
A30 road at St. Mark's Roundabout, before separating in a north-easterly direction to follow the entire length of the
River Bourne. It has a grade-separated junction with the main
A303 road and then passes through the town of
Tidworth. From there the road travels north to
Collingbourne Ducis, where it twists through the village around the church to a mini-roundabout. It turns left to continue northwards alongside the Bourne through another narrow stretch at
Collingbourne Kingston to another mini-roundabout before again heading north. Near
Burbage the continued route north to
Swindon is designated
A346, the A338 turning off to the right at a roundabout and heading east then north-east and crossing the border into
Berkshire. It passes through the town of
Hungerford, where it meets the
A4 road (to
Marlborough and
Newbury). It meets the
M4 motorway at junction 14, passes through the village of
Great Shefford and crosses into
Oxfordshire. It goes through
Wantage where it meets the
A417 road, and past the villages of
Grove,
East Hanney and
Frilford. It terminates at its junction with the
A420 road near
Bessels Leigh, south-west of
Oxford. ==History==