A man who fell off a bridge over the M1 has died, along with another man who went to his aid.
Emergency services were called to the northbound carriageway near junction 5 at around 10.45am after reports a man had fallen from the bridge.
A number of motorists pulled over to assist but one of the drivers was struck by an oncoming vehicle. Both men were pronounced dead at the scene.
The road was closed for several hours and drivers were diverted from the affected stretch of motorway while investigations took place at the scene, but all lanes have since reopened.
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.
Police are appealing for witnesses to call Hertfordshire Police non-emergency number 101 quoting ISR 176 of 30 January.