London Ambulance Service has confirmed the A40 at Hillingdon has been closed after a woman fell from the Swakeleys flyover.
The woman died at the scene. The Met Police say she was in her 20s and next of kin have been informed.
Four motorists were treated on the spot by ambulance crews but did not need to go to hospital.
Large queues have formed in the area in both directions.
Police accident investigators are still on the scene (6.35pm) and the eastbound carriageway is still closed from the M25 to Swakeleys Roundabout. It is not known how long it will be closed.
Police say a the woman was struck by a number of vehicles after she fell onto the road and they have appealed for witnesses who may have seen her before she fell to call 020 8991 9555.
The tragedy comes just days after a teenager was rescued from the same spot by a police officer in his first week at work.
London Ambulance Service said it was called at 4.05pm to reports of a person falling from height on to the London-bound carriageway below the Swakeleys flyover.
A spokesman said an ambulance, single responder and a duty officer were all dispatched to the scene.
Reaction to the death has come in via the getwestlondon.co.uk and uxbridgegazette Facebook pages.
Cassandra Dunstan Wigfield said: "So very sad for her and her family."
Stephanie Preston said: "That poor lady, how awful."
