London Buses route SL9

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 RATP Dev Transit London.

The route partially parallels routes 140 and 278.

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between Harrow and Heathrow Central bus stations and as a partial replacement for the all stops route 140, which was withdrawn between Hayes & Harlington and Heathrow at the same time. 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. However, due to delays in the delivery of new Alexander Dennis Enviro400EVs and the refurbishment of the Wright SRM bodied Volvo B5LHs for the route, London Sovereign initially operated it with Wright Gemini 3 bodied Volvo B5LHs.

On 26 August 2023, route X140 was renumbered SL9, becoming part of the Superloop network of orbital express bus routes.

Current route
Route SL9 operates via these primary locations:
 * Heathrow Central bus station
 * Harlington
 * Hayes & Harlington station
 * Hayes
 * Yeading
 * Northolt station
 * Northolt Park station
 * South Harrow station
 * Harrow bus station for Harrow-on-the-Hill 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.