Police are appealing for witnesses, information and dash cam footage following a collision in Brookmans Park.
The incident occurred just before 4.30pm (Sunday 7 October) on Cum Cum Hill.
A grey Toyota and a grey Kia were involved.
Five people were taken to hospital, four with slight injuries and one with serious injuries which are not believed to be life threatening.
PC Ryan Jackson, from the Bedfordshire, Cambridgeshire and Hertfordshire Road Policing Unit, said: “Enquiries are underway to understand the circumstances of the collision.
“I am appealing to anyone who was travelling in the area at the time and may have witnessed what happened, or the events leading up to it, to please contact us. If you have a dash cam fitted, please review your footage as you may have captured something that could assist with our investigation.”
Anyone with information can contact PC Jackson via email.
You can also report information online, speak to an operator in our Force Communications Room via our online web chat or call the non-emergency number 101, quoting ISR 472 of 6 October.
Alternatively, you can stay 100% anonymous by contacting the independent charity Crimestoppers on 0800 555 111 or via their untraceable online form.
If you have dash cam footage in relation to the collision, please upload to DAMS.