Traffic is building on the A1(M) after the road was closed due to a fault in overhead cables.
The road is closed in both directions between Junction 7 and 8 for Stevenage.
There are delays of up to 30 minutes on the northbound carriageway, and 12 minutes southbound - which are expected to increase.
The closure is also causing delays on the A602 Coreys Mill roundabout in Stevenage as traffic is diverted.
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