Motorists travelling westbound on the M4 are facing delays after a collision involving a car and a lorry between Brentford and Heston.
Police officers, London Ambulance Service (LAS) and London Fire Brigade (LFB) are on the scene but all services have been unable to confirm the condition of the motorists involved.
All lanes have been reopened although drivers have been warned of very slow traffic.
The woman died at the scene in Uxbridge Road in Iver which happened shortly before 7.50pm.
Police are appealing for witnesses as they try to establish the cause of the crash.
Investigating officer, sergeant Tom Smith from Thames Valley Police, said: "I would like to appeal for anyone who witnessed this incident, or who has any information relating to it, to contact us on 101."