GWR will be making its biggest timetable change in December, said to be the most comprehensive since the introduction of HSTs in 1976.
More than 75% of the timetable is changed or recast, with faster journeys taking advantage of the superior IET acceleration times, more frequent trains and extra seats.
GWR says there will be more enhancements next May.
Coming are extra services to the West of England, with core services to Plymouth or Penzance running non-stop between Reading and Paignton, and a semi-fast service for intermediate stations to Exeter.
Additional peak trains will run between London and Bristol and also London to Swansea, the latter non-stop from Paddington to Bristol Parkway.
A two-trains-per-hour off-peak service from Temple Meads to London is also in the pipeline, but with no start date fixed.
South Cotswold services to Cheltenham become hourly, as does the North Cotswold route to Worcester, with additional peak trains. IETs will run to Banbury, with a morning and evening peak service.
Transport for London will take over Reading to Paddington local trains, with two per hour, while GWR Class 387s will operate semi-fasts.
Journey time cuts see the fastest London to Bristol time of 79 mins, but most will take 84; the fastest Cardiff train will be 102 mins, others 113, while the fastest Up Penzance train will take a minute under five hours.
GWR managing director Mark Hopwood said the Class 80x IETs were outperforming HSTs by around 10k miles, in respect of reliability and miles per technical failure, which gives the company confidence for the improved timetable.
Its PPM measure and moving annual average at 90.8% and 89.14% for the latest periods continues the improving trend. GWR has taken on more than 140 additional drivers and trained 1,400 on new traction types.
The IETs will be getting the latest versions of software, which are already in use by LNER and TransPennine, and while it is still planned to run through the Severn Tunnel on diesel power, there is an aim to run IETs to Newport from the first week in January, and subject to approval, to Cardiff soon afterwards.
GWR is due to replace the Heathrow Express Class 332s with specially modified Class 387s, with one set having been on ETCS test. It is planned to test this set and a TfL Class 345 set in the Heathrow tunnels in January.
Delays introducing the tri-mode Class 769s to GWR has made progress, with Northern having accepted a set after 2,000 miles running on diesel fault free.
Two more sets are about to be accepted, and this opens the way for completion of the Northern order, followed by the nine sets for Transport for Wales, and then GWR taking delivery of their sets from early summer.
At Exeter, the £40million depot is progressing, and is the biggest investment First
has made in a depot, with a three-road maintenance shed for five-car trains, stabling, fuelling and train wash.
Discussions are on-going with Network Rail into extending the platform two bay to accommodate five-car trains as both GWR and CrossCountry are proposing more Exeter starting and terminating trains.
Investment in stations has not been overlooked, with Bridgwater, Moreton-in-Marsh, Handborough, Didcot and Pershore getting upgraded, and Worcestershire Parkway due to open in mid-December. GWR has also bought land at Castle Cary to create new car park.
GWR is also looking at its contingency plans, a depot review, provision of critical services, and prioritising set availability. There will also be an emphasis on right-time dispatch, with staff practicing coupling/uncoupling of five-car IETs at Temple Meads.
Read more News and Features in the December 2019 issue of The Railway Magazine –on sale now!
Enjoy more of The Railway Magazine reading every month. Click here to subscribe.