Great Western Railway electrified line goes live
Trains have begun operating on new sections of electrified line on the Great Western Railway.
Work on the track between Reading and Newbury, and Swindon and Bristol, has been plagued with problems, including delays and spiralling costs.
It is part of plans to modernise the Great Western mainline.
Network Rail thanked passengers for their patience while it "delivered the biggest modernisation of Brunel's railway since it was built".
James Davis, from Great Western Railway, said the work had enabled the company to bring into service "600 more carriages than we did 18 months ago".
He said: "Our new inter-city express trains have up to 24% more seating capacity, and in the fullness of time once that electrification work has been completed, we will start to see frequency improvements and quicker journey times."
The £2.8bn scheme was also set to include the main line to Oxford, Bath and Bristol, but some parts were "deferred" in 2016 following rising costs.
In July last year the government announced the planned upgrade of the line between Swansea and Cardiff had been scrapped altogether.
The full route to Cardiff is due to be finished this year.