Two of the slowest bus routes in London go through Hornchurch. Information about the average speed of buses has recently been released by TFL and the slowest buses were worked out by urbs.london using this information

Central London congestion is blamed for the slow down in buses, now running at an average speed or 9.3 mph.  But the 650 and 656 buses, both leaving from Emerson Park School are running at just 6 miles per hour and are among the 10 slowest routes run by Transport for London in the last financial year.

image
656 bus route: Google maps via TfL

656 from Emerson Park School to Gallows Corner, Hornchurch travelling at an average of 6.1mph

image
650 bus route: Google maps via TfL

650 from Emerson Park School to Cedar Hill, Hornchurch travelling an average of 5.9mph

TfL runs 675 routes and tracks the speed of buses each way along them, plus night buses.   Of the 1762 bus routes speeds recorded for the last financial year, 563 were below the 9.3 mph average.  Most of the slowest journeys cross central London.

London’s 10 slowest buses
15H – Charing Cross to Tower – 4.9mph
15H – Tower to Charing Cross – 5.1mph
14 – Putney Heath to Warren St Station – 5.6mph
11 – Liverpool St Station to Fulham Broadway – 5.6mph
650 – Emerson Park School to Cedar Hill, Hornchurch – 5.9mph
11 – Fulham Broadway to Liverpool St Station – 5.9mph
26 – St Mary of Eton, Hackney to Waterloo Station – 6.0mph
69A – Canning Town to Walthamstow Bus Station – 6.0mph
38 – Clapton Pond to Victoria Bus Station –
6.1mph
656 – Emerson Park School to Gallows Corner, Hornchurch – 6.1mph