The Red Arrow Transit is a electric bus rapid transit system which started around the 1990's it was initially operated by London General from their Waterloo garage using Leyland National 2s.
In 2002 routes 507 and 521 was converted to low-floor single deck articulated operation using Mercedes-Benz 0530 Citaro's.
In 2009 the Mercedes-Benz articulate's were replaced with 12.0 metre Mercedes-Benz 0530 Citaro's  and the Weekend allocation was transferred to Mandela Way (MW).
In 2013 brand new BYD Electric demonstrators were introduced.
In 2015 brand new Irizar I2 EV's were introduced.
In August 2016 route 507 and 521 was retained by London General using brand new Enviro200 MMC bodied BYD K9Es.
In January 2017 the routes was converted to full Enviro200 MMC bodied BYD K9E.
 The routes partially transferred to London Central from their Camberwell (Q) garage replacing Mandela Way (MW) allocation from 29 July 2017.
Current route London Buses Route 507
- Victoria bus station
- Horseferry Road
- Lambeth Bridge
- St Thomas Hospital
- Waterloo Station Taxi Road
Current route London Buses Route 521
- Waterloo Station Taxi Road
- Waterloo Bridge
- Holborn
- St Paul's
- Cannon Street Station
- London Bridge Station