Delays are expected on the M4 westbound due to an accident involving two cars.
One lane has been closed between J5 for Langley and J6 for Slough.
Traffic is also building up on the London bound carriageway between J10 for Wokingham and J5 for Lanlgey.
Travel time is estimated at 65 minutes with traffic travelling at an average of 15 miles an hour.
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The Met Office has issued a yellow alert for Windsor and Maidenhead, Slough and Wokingham, warning that rain moving eastwards across the south of the country may turn to snow in some places.