A road closure is in place from M1 Junction 8 for Hemel Hempstead to the Park Street roundabout on the A414 following a serious collision.
Herts police are currently at the scene near the Park Street roundabout on North Orbital Road, St Albans.
The fire and ambulance services are also at the scene.
Officers expect the road to be closed for some time and are asking people to avoid the area where possible and plan an alternate route.
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