A 20-year-old man died on Christmas Eve after a car plunged down an embankment.
Hertfordshire Police said the incident took place on the A1081 London Colney Bypass near St Albans at about 2330 GMT on Wednesday.
The man, from Smallford, was behind the wheel of a blue Peugeot 205 heading south towards the Bell roundabout at Junction 22 of the M25.
He lost control of the vehicle by the Lowbell Lane bridge.
The unidentified man died at the scene and his passenger, a man from St Albans, is in a critical condition at Hemel Hempstead Hospital.