Drivers heading towards Bristol from Gloucestershire face disruption this morning after a serious collision shut the M4 westbound between Junction 16 (Swindon West) and Junction 17 (Chippenham). The carriageway remains closed while police carry out investigation work, with diversions signposted and delays likely through the morning.
What we know so far
The incident happened at about 8.05pm on Saturday and is understood to have involved a car and a van. Several people required hospital treatment. Emergency services — including Wiltshire Police, the ambulance and fire services, and National Highways officers — attended. Eastbound traffic was briefly held to allow two air ambulances to land; those vehicles were released shortly after 10.30pm. The westbound side has remained shut overnight and into Sunday morning while a complex collision investigation takes place.
“Road closed due to crash investigation work on M4 westbound from J16 A3102 Swindon Road (Swindon West) to J17 A350 (Chippenham). The closure is expected to remain in place for some time following a serious accident. Detour in operation.”
That statement, from the AA’s live traffic service this morning, reflects the continuing disruption as officers examine the scene.
Official diversion for most vehicles
National Highways has issued a signed route for vehicles under 4.2m in height, using the solid diamond symbol on roadside signs. The agency advises motorists to:
- Exit at J16 and keep left on the slip road, continuing straight at the lights to join the A3102 towards Royal Wootton Bassett.
- Stay on the route for around two miles to the roundabout with the B4042 at Royal Wootton Bassett.
- Take the second exit onto the B4042 and continue for about nine miles, passing The Common and Brinkworth, to the Priory Roundabout with the A429.
- Turn left onto the A429 and follow it for roughly five miles to rejoin the M4 at J17.
National Highways also notes that separate guidance applies to vehicles of 4.2m and above; drivers of taller vehicles should follow on-road signage and any instructions from traffic officers.
Why it matters for Gloucestershire
Although the scene is in Wiltshire, this section of the M4 is a key link for many in Gloucestershire travelling to and from Bristol, North Wiltshire and the wider South West. The westbound closure between Swindon (J16) and Chippenham (J17) means anyone returning from the east — including drivers coming down the A417/A419 corridor from Cirencester towards the M4 — may encounter diversions, extra traffic on local roads and longer journey times this morning.
| Key point | Detail |
|---|---|
| Location | M4 westbound, J16 (Swindon West) to J17 (Chippenham) |
| First reported | Around 8.05pm, Saturday |
| Status | Westbound carriageway remains closed for police investigation |
| Emergency response | Police, ambulance, fire, National Highways; two air ambulances attended |
| Diversion symbol | Solid diamond, via A3102 → B4042 → A429 |
Travel advice
With investigation work expected to continue for “a considerable time”, motorists are urged to plan ahead and check the latest updates before setting off. In practical terms:
- Allow extra time for journeys towards Bristol and North Somerset if travelling from east of Gloucester and Cheltenham.
- Follow the signed diversion route between J16 and J17 rather than using minor lanes, which can become quickly congested.
- Monitor live updates from National Highways, the AA and local police for reopening times and any changes to the diversion.
What happens next
Wiltshire Police has described the investigation as complex. While no reopening time has been confirmed, National Highways expects the closure to remain in force while collision investigators complete their work and recovery teams make the carriageway safe. Drivers should look for on-road signals and traffic officer guidance as conditions change.
We’ll keep this story updated as further details are confirmed, including any timetable for reopening and advice for higher vehicles once issued by National Highways.
