Rail electrification: Faster trains to start 'by 2018'
Passengers will benefit from faster train services between Swansea and London by 2018 when work to electrify the line will be completed.
Network Rail says modernising one of the busiest lines into south Wales will cut 20 minutes off the three-hour journey.
A £350m investment will also see lines from Cardiff to the south Wales valleys electrified.
However those lines may not be ready until about 2020.
The south Wales rail electrification, and the prospect of longer, faster trains, was announced last summer by the Department of Transport
But Tuesday sees the first official timetable given by Network Rail which will be building the line.
BBC Wales business correspondent Nick Servini reports.