Three people had to be cut from cars after a two vehicle smash on Saturday night.
Emergency services were called to Midland Road in Hemel Hempstead just after 7pm.
The road had to be closed while firefighters worked to free those trapped in the cars.
Four people were taken to hospital by ambulance.
Both vehicles, a red Mini Cooper and a blue Subaru Impreza had to be recovered.
The road was re-opened just after 9.30pm.