Motorists were stuck in sweltering heat on the M25 after a lorry carrying fibre glass caught fire closing part of the motorway.
Two lanes of the anti-clockwise carriageway were closed after the articulated lorry caught alight at about 0650 BST on Friday.
There was concern that the consignment of fibre glass might have released dangerous particles into the air.
Traffic was slowly returning to normal by Friday evening when all four lanes had re-opened but remained slow between junctions eight and 13.
Seven-mile tailback
Officers from Surrey Police gave out water to drivers who were stuck in the queues.
Motorists had to be diverted through Leatherhead in Surrey because of the incident which happened between junctions nine and eight.
A Surrey Police spokeswoman said there was a seven-mile tailback at midday between junctions 10 and 12.
Drivers were advised to avoid using the motorway on Friday if at all possible.
Surrey Fire Brigade sent at least five vehicles including two water carriers to help tackle the fire.
A brigade spokeswoman said half of the lorry's contents was damaged.