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At a glance

🕐 Last verified 21 Mar, 12:24

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StatusLive
Severity (NH)Severe
RoadM4
DirectionWestbound
RegionSouth West
Category (NH)Crash
ReportedSat 21 Mar, 12:24
Road typeMotorway
Speed limit70 mph (variable)
Weather☁️ Overcast
ReferenceREF-25576498
Views126

Times are UK time.

What National Highways say

M4 westbound between J20 and J21 | Westbound | Accident

Location : The M4 westbound between junctions J20 and J21 . Lane Closures : Lane two is closed. Reason : Road traffic collision. Status : Currently Active. Time To Clear : The event is expected to clear between 13:15 and 13:30 on 21 March 2026. Return To Normal : Normal traffic conditions are expected between 14:15 and 14:30 on 21 March 2026. Lanes Closed : There is one of two lanes closed.

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2 updates captured · Cleared

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M4  · Westbound J20 to J21 ✓ CLEARED

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Also on the M4 today

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Recent M4 incidents

182 incidents and roadworks logged on the M4 in the last 30 days, 56 of them serious or severe. Times are UK time.

M4 | Berkshire | Carriageway Closure | DelaysWed 9 Sep, 21:42 M4 | Berkshire | Carriageway Closure | Long Delays 30 minutesWed 9 Sep, 21:42 M4 | Greater London | Carriageway ClosureWed 9 Sep, 01:27 M4 | Gloucestershire | Road Closure | Expect DelaysWed 2 Sep, 22:45 M4 | Wiltshire | Carriageway Closure | Expect DelaysSat 15 Aug, 02:59 M4 | Wiltshire | Carriageway Closure | Expect DelaysThu 6 Aug, 09:35
Every M4 incident

Common questions

Is the M4 closed?

Not fully. There were lane closures on the M4 westbound J20 to J21 at 16:46 UK time on Tue 3 Nov 2026. See the M4 right now.

What happened on the M4 on 21 Mar 2026?

Crash on the M4 westbound J20 to J21 in the South West, reported at 12:24 UK time on Sat 21 Mar. Lane closures. Still live.

Where can I see everything else on the M4?

The M4 live page shows what is happening now, and the M4 archive has every incident on record.

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