COMMUTERS faced gridlock on Monday after a mystery diesel spillage was spotted by road-users.
Police received multiple calls from about 7.30am onwards, and Herts Highways were called to tackle the clean-up operation.
Gritters put sand on the affected areas to make the roads safe again.
The fuel had been spotted in Maylands Avenue, Swallowdale Lane and Warners End Road - all in Hemel Hempstead.
But neither police or highways chiefs could identify what had caused the spillage.
Spokesman Andrew Dawson said: “I am assuming it was a spillage from a vehicle and they did not realise it was going on.
“It was not a big slick of diesel. It was just a splattering on the roads.”
It is the second time Hemel Hempstead has faced roads gridlock in a fortnight.
Streets including Queensway and Leighton Buzzard Road were brought to a near-standstill two weeks ago after an engine blaze in a lorry on the southbound entry sliproad to the A41.