Police investigating the scene of the incident on the M1
A man died when he fell from a bridge over the M1 in Hertfordshire and a Good Samaritan driver who came to his aid was then killed by a passing vehicle.
Emergency services were called to the Bucknalls Lane bridge over the motorway near Watford at 10:45 GMT.
The motorway was shut for several hours and has now reopened. Police want to hear from witnesses, a spokesman said.
Motorway CCTV footage showed emergency services on the bridge above the scene of the incident and on the road below.
A spokesman for the East of England Ambulance Service said two ambulances, an emergency response vehicle and an air ambulance had been dispatched to the scene but were stood down after midday.