The Hatfield Tunnel and Cavendish Way, which runs above the motorway, were closed for more than half an hour
There is a severe disruption to traffic both ways on the A1 this morning due to an earlier police incident.
Long delays are to be expected between junction 4 for A6129 Hertford and junction 3 for A1001 St Albans Hatfield, affecting junction 6 for B656 Welwyn Hertfordshire.
The Hatfield Tunnel and Cavendish Way, which runs above the motorway, were closed for more than half an hour. It reopened just before 7.30am.
Alternative routes should be considered.
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