A motorcyclist was airlifted to hospital after he crashed into the central reservation of the A1.
The crash happened shortly after 1.20pm on Sunday on the southbound carriageway between the M25 and Borehamwood.
The rider, who is in his 50s, was travelling on a red Honda motorcycle when he collided with the barrier in the middle of the road.
He sustained serious injuries and was taken to hospital by helicopter.
The man remains in hospital seriously injured. His next of kin have been informed.
Police have launched an investigation into the crash. At this stage, officers have yet to determine why the rider crashed into the central reservation.
The crash scene is believed to have been shortly after the Galley Lane junction of the A1.
The southbound carriageway was closed for several hours.
Sergeant Tim Davies, from the Bedfordshire, Cambridgeshire and Hertfordshire Road Policing Unit said: "I am appealing for anyone who witnessed the collision, or saw the motorcycle prior to it, to please get in touch. I’m particularly keen to hear from anyone who may have captured dash cam footage."
Anyone with information is asked to email timothy.davies@herts.police.uk or call 101 quoting ISR 372 of Sunday 11 July.
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