The below charts show how the reliability of services on the Severn Beach Line has changed since May 2017. This includes cancellations, and groups the short-delay trains (1-4 minutes) with on-time trains.

Severn Beach Line Reliability - since January 2020
Severn Beach Line Reliability – since January 2020
Noteworthy causes of service disruption/improvement since January 2020:
August 2021 – Bristol East Junction engineering over-run on weekend of 14th/15th August resulted in 56 cancellations
July/August 2021 – Bristol East Junction engineering from 10th July-3rd September, on some Sundays services replaced by buses, on some days services terminated/started at Lawrence Hill
January 2021 – announcement of lockdown #3 from January 5th onwards, GWR says it will continue to run the December temporary timetable
December 2020 – new timetable with later services on Sunday mornings for Temple Meads engineering, also GWR staff shortages due to Covid-19 result in temporary timetable over Xmas and new year
November 2020 – announcement of lockdown #2  from November 5th-December 2nd
July 2020 – full timetable resumed from Saturday 11th July with 46pd on Saturdays – passenger numbers rising
May 2020 – service increased from Sunday 17th May – 26pd Sunday, 32pd Saturdays, 50pd weekdays, still very low passenger numbers due to Covid-19
April 2020 – official Covid-19 timetable introduced Monday 30th March – service reduced to 26pd Sunday, 32pd Saturdays, 26pd weekdays (28pd weekdays from 13th April)
March 2020 – at least 118 of these 134 cancellations were “planned cancellations”  for GWR interim emergency Covid-19 timetable from 23-27th March (start date of lockdown #1)

Severn Beach Line Reliability - May 2017 to December 2019
Severn Beach Line Reliability – May 2017 to December 2019
Noteworthy causes of service disruption/improvement for May 2017 to December 2019:
December 2019 – increase in IET London service frequency
December 2018 – services are routed via four-tracks on Filton Bank
Autumn 2018 – Filton Bank blockade 27th October to 18th November plus weekends of 13th/14th Oct, 24th/25th Nov, 1st/2nd Dec
Summer 2018 – several weekends of engineering bustitution
July 2018 – Network Rail complete BASRE/ARS tweaks to improve SBL regulation
Spring/Summer 2018 – GWR introduce measures to improve Turbo 166 performance on SBL, e.g. intermediate door controls
April 2018 – Network Rail (NR) complete Bristol Area Signal Renewal & Enhancement with some disruption to SBL services
March 2018 – SBL problems due to snow
July 2017 – issues with introduction of Turbo 166s

“Late” =  services 5 or more minutes late on arrival at Severn Beach Line destination northbound, or Severn Beach Line destination southbound, ie, not beyond Bristol Temple Meads
“Cancellations & turnbacks” =  includes services cancelled throughout,  services turned back prior to (or started after) scheduled stations and services that skipped scheduled stops
“On Time” = services run to time or less than 5 minutes late
This data has been collected variously from realtimetrains, raildar and recenttraintimes, none of which guarantee 100% accuracy.  (AM/TM/CJD)
Number of services run per month depends on month length, weekdays in a month, extra summer Sunday services and scheduled timetable changes for engineering