Plan extra time during rush hour; roads leading to Heathrow, including the M4, often experience congestion

https://www.scribd.com/document/1074929924/National-Rail-to-Heathrow-Routes-Transfers-and-Tickets-Explained-232993

Plan extra time during rush hour; roads leading to Heathrow, including the M4, often experience congestion, especially around junctions and airport exits.