Commuters using the Elizabeth line are facing disruption throughout Wednesday due to defective track in west London.
A speed restriction is in place at Hayes & Harlington is causing delays to journeys through the station.
The issue is also affected Great Western Railway and Heathrow Express services.
National Rail says the disruption is expected to last all day.
Meanwhile the Central line was hit with an early-morning suspension and severe delays following a late finish to engineering work.
