Passengers are being urged to check before they travel between Newport and Shrewsbury as Network Rail embarks on upgrade works over six consecutive weekends beginning on 11 June.
Network Rail says there will be significant work at Shrewsbury station and signalling upgrade work in and around Hereford station. The work finishes on Sunday, 17 July.
Bus replacement services will be running during work between Newport and Shrewsbury, with the exception of Saturday, 9 July when trains will be running between Newport and Hereford because of the World Speedway Championships at the Principality Stadium in Cardiff.
Network Rail has released a time lapse video of three months work on the Cardiff Road bridge in Newport.
It shows the largest telescopic crane in the UK which was used during the works.
The video was filmed from December 2015 until February this year, as engineers raise the height of the bridge creating the room for the overhead wires needed to power new electric trains.
Network Rail says a new footbridge has opened as part of an £11m upgrade at Port Talbot Parkway Station.
The 400-tonne bridge aims to provide better step-free access to the public across Port Talbot.
It houses a new ticket office, waiting area, customer facilities and CCTV equipment, as well as steps and lift access to platforms.
The Welsh Government has welcomed today's announcement of changes to Network Rail but says there should be no delay to plans to electrify the line from London to Swansea. A spokesperson says:
Opposition parties are demanding that the Transport Minister confirms that the Great Western main line will still be electrified through to Swansea by 2018. Patrick McLoughlin told MPs that the project was a top priority and is going ahead when other electrification schemes are being "paused". But he told Plaid Cymru's Jonathan Edwards that he'd have to write to him about the completion date.
Mr Edwards said he was "concerned by the ambiguity" of the minister's response. The Liberal Democrats' spokesperson in the Assembly says she'll also be writing to Patrick McLoughlin.
But the Wales Office Minister Alun Cairns has backed today's announcement.
Transport Secretary Patrick McLoughlin has told MPs that the electrification of the Great Western main line will be prioritised over other projects in the midlands and north of England as part of a crackdown on delays and rising costs at Network Rail. The state-owned company which controls the railway tracks is due to electrify the line from London to Swansea.
The minister told Plaid Cymru MP Jonathan Edwards that the government remained committed to electrifying through to Swansea on schedule, though he couldn't confirm that meant by 2018. He did not mention the electrification of the Valley Lines, which will largely be funded through the Welsh Government.
Network Rail say the go-ahead for rail electrification in the Valleys will mean a better train service and boost the Welsh economy.
Figures show that despite most people agreeing it’s dangerous to trespass on railway tracks, a third believe they would hear a train in time to move out of the way.
This increases to more than half of 16-24-year-old males.