Electrification of the rail route between Preston and Manchester is not expected to be completed until 2018 – more than a year later than planned, according to a report seen by the BBC.
Network Rail has said that “poor ground conditions… from old, known and unknown, underground mine workings” were delaying progress.
Construction for the upgrade began in 2015 and was scheduled to be completed by the end of 2016 but that was changed to December 2017 and a spokeswomen from Network Rail told the BBC that the work is now due to complete in 2018. She said they were “delivering improvements to northern railways not seen since the Victorian times” but it was “taking longer in practice than we had hoped it would”.
“One unforeseen factor adding time to our programme are the poor ground conditions we face from old, known and unknown, underground mine workings.”
Network Rail believe “numerous locations” along the route, which is nearly 180 years old and one of the busiest in north west England, are affected.
It said engineers were “working hard” to solve the problem but rail journeys would continue as usual.
Network Rail has been contacted for further comment but has not yet responded.