Heathrow Airport Holdings
The service runs along Network Rail's Great Western Main Line from Paddington to Airport Junction. The line from Airport Junction to the airport terminals is owned by Heathrow Airport Holdings but maintained by Network Rail. The line is electrified at 25 kV AC overhead and uses Automatic Train Protection (ATP). The controlling signal box for the entire route is the Thames Valley Signalling Centre (TVSC) in Didcot.