London Buses route SL9, formerly London Buses route X140, is a Transport for London contracted Superloop express bus route in London, England. Running between Heathrow Central and Harrow bus stations, it is operated by First Bus London subsidiary London Sovereign.
History The route commenced on 7 December 2019, originally numbered X140, as part of a reorganisation of routes in the lead up to the opening of the Elizabeth line. Route X140 was introduced as a limited stop service between Harrow and Heathrow Central bus stations and as a partial replacement for the all stops route 140, which was withdrawn between Hayes & Harlington and Heathrow at the same time.New route X140 - Limited stop service between Harrow and Heathrow Airport Transport for London 7 December 2019RTs return to Heathrow for route 140 farewell Buses issue 778 January 2020 page 22 Route X140 was initially operated by Metroline.
Upon being put out to tender, on 4 September 2021 route X140 was taken over by London Sovereign's Harrow bus garage.TfL contract awards give boost for zero-emission operation Route One 3 November 2020Latest tendered service awards Buses issue 789 December 2020 page 21 However, due to delays in the delivery of new BYD Alexander Dennis Enviro400EVs, London Sovereign initially operated it with existing hybrid double deckers.RATP shuffles fleet Buses issue 800 November 2021 page 22
On 26 August 2023, route X140 was renumbered SL9, becoming part of the Superloop express bus network.Third London Superloop route to start as X26 becomes SL7 Route One 18 August 2023Route X140 renumbered - 26 August 2023 Transport for London
On 28 February 2025, the route passed from London Sovereign to First Bus London following the acquisition of RATP Dev Transit London by FirstGroup.
Current route Route SL9 operates via these primary locations:Route SL9 Map Transport for London Heathrow Central bus station Harlington Hayes & Harlington station Hayes Yeading Northolt station Northolt Park station South Harrow station Harrow bus station
Operation The route operates at a frequency of a bus every 12 minutes on weekdays and Saturdays and a bus every 15 minutes on Sundays. Between the hours of 23:00 and 07:00, the route is covered by an all stops night service, numbered N140, running every 30 minutes between Harrow Weald bus garage and Heathrow Central bus station.
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