Officers are appealing for information, witnesses and dash cam footage following a fatal collision in Tring.
The incident happened on the A4251 at around 10.30pm on Friday, December 24.
One vehicle was involved – a white 1979 Volkswagen Polo, which collided with the central island and a lamppost.
The front seat passenger – a woman in her twenties – sadly died. Her family are being supported by specially-trained officers.
The driver – a 26-year-old man from Hemel Hempstead – was arrested on suspicion of driving under the influence of cannabis and causing death by dangerous driving. He remains in custody at this time.
Sergeant Simon Cooper, from the Bedfordshire, Cambridgeshire and Hertfordshire Road Policing Unit, said: “Our thoughts are with the victim’s family, who have lost their loved one so close to Christmas.
“I am appealing for anyone with information to get in touch. The vehicle, being a 1979 model, is very distinctive so hopefully there are a number of witnesses. Did you see the collision or the events leading up to it?
“If you think you might have caught what happened on dash cam, please review it and let us know. Any information you have, no matter how small it might seem, could be vital to our investigation.”
You can report information online at herts.police.uk/report, speak to an operator in the Force Communications Room via the online web chat at herts.police.uk/contact or call the non-emergency number 101, quoting Op Leonid.
Alternatively, you can stay 100% anonymous by contacting the independent charity Crimestoppers on 0800 555 111 or via their untraceable online form at crimestoppers-uk.org.