Drivers were stuck in queues for more than an hour after a gas leak from a tanker closed the A1(M) in County Durham.
The motorway was shut northbound between junction 63 for Chester-le-Street and junction 64 for Washington on Thursday morning after a "transporter vehicle" carrying nine hydrogen gas cylinders was found to be leaking.
County Durham and Darlington Fire and Rescue Service sent a crew from High Handenhold to carry out risk assessments and a specialist engineer was called to make sure the cylinders were safe.
One of the cylinders was found to be cracked and leaking and the other eight cylinders were also affected.
The only way to deal with the incident was to allow the cylinders to vent and the tanker could not be moved due to the flammable nature of hydrogen.
Originally the entry slip on to the A1(M) was closed but the entire carriageway was shut down from 4am on Thursday.
Officers from Durham Constabulary assisted in the road closure, which caused traffic queues several miles long with delays of up to 90 minutes.
Southbound traffic was unaffected and diversions for northbound traffic were put in place using the A167, Vigo Lane and the A195.
The carriageway was reopened at just before midday.
A spokesperson for the fire service said: "The ongoing incident on the A1 motorway between Chester-le-Street and Washington has now finished.
"The specialist team have made the transporter safe and the A1 northbound carriageway has now reopened."
