Emergency services were called to a serious collision on Redbourn Road in St Albans.
Officers from Herts police and the Beds, Herts and Cambs road policing unit were called to the scene at around midnight.
Redbourn Road is still closed in both directions, between the A4147 Bluehouse Hill roundabout and Redbourn, while emergency services deal with the incident.
Drivers are advised to avoid the area and seek alternative routes.
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