Network Rail has postponed work to upgrade the Brighton Main Line after a recent timetable change caused months of rail chaos.
A planned nine-day closure of the line in October has been cancelled and some parts of the work have been deferred to the next funding period, which starts in April next year.
The decision will allow passengers to “plan ahead”, Network Rail said, after the unsuccessful implementation of a new Thameslink timetable led to mass delays and cancellations.
Improvement works will focus on four Victorian-era tunnels – Balcombe, Clayton, Patcham and Haywards Heath – to stem leaks, provide reliable drainage and upgrade track, third rail power systems and signalling.
Network Rail South-East managing director John Halsall said: “I know many passengers have had a really tough time since the timetable change in May.
“That’s why I asked for a review of all our planned maintenance and improvement work with GTR to identify any opportunities to postpone or re-plan engineering work to a later date.
“I’m pleased we’ve been able to re-plan the way we’re carrying out this long-overdue upgrade to one of the most unreliable parts of our rail network, meaning passengers will get almost all of the reliability benefits but with significantly less weekday disruption.
“I’d urge passengers to plan ahead and we’ll continue to work closely with the train operators, Transport Focus and passenger groups to make sure the travelling public gets the best possible service during the closures.”
The announcement comes as the TSSA union leader Manuel Cortes warned that driver shortages would cause more cancellations as an interim rota comes into effect on Thameslink routes.
A nine-day closure to complete the works will go ahead between 16 to 24 February as planned, as will 15 weekend closures between September and May.