Motorists in the west of England and north of London faced delays after a string of motorway accidents and incidents on Monday.
A man was killed in a collision involving two lorries on the eastbound M4, causing all three lanes to be closed between junctions 22, for the second Severn crossing, and 20, the Almondsbury interchange.
Two men died in an accident involving two black BMWs on the M1 near Watford, leading to a section of the motorway being closed in both directions. The road reopened later.
Avon and Somerset police advised motorists to avoid the area around the scene of the M4 crash, which happened at 8.40am. A spokesman said: "Traffic is advised to avoid the area if at all possible and find alternative routes as the section of the motorway is likely to be closed for a significant part of the day."
Drivers travelling from the west along the M4 were advised to use the M49. But the problems were compounded by an accident on the southbound part of the M49 between the M4 and M5, although the vehicle involved was moved to the hard shoulder.
There was also congestion on the M5 northbound past junction 17 after an accident involving a car and lorry blocked one lane in the roadworks there. And a vehicle fire caused the closure of two lanes on the westbound side of the M4 between junctions 19 and 20. Traffic was queuing back to junction 18 of the M4 and junction one of the M32, which links Bristol city centre to the M4.
The M1 collision happened shortly before 2.40am on the southbound carriageway between junctions five and four, near Watford. A male driver and his front-seat passenger were killed, and two male passengers were taken to St Mary's hospital in Paddington, central London, with "serious injuries", a Hertfordshire police spokeswoman said.
Two men travelling in the other BMW were being treated in Watford general hospital. Their injuries were not thought to be life-threatening, she said.
An investigation is under way to determine the cause of the crash. Five junctions of the motorway were closed in both directions; the northbound carriageway reopened in the morning and the southbound by lunchtime.