Some major sections of the rail network will be shut down over the Christmas and new year period because of engineering work, Network Rail (NR) confirmed today.
The most disruption will be on lines from London into South Wales, while there will also be disruption in the Southampton area.
There will be 28 separate pieces of engineering work on Sunday December 27 while there will be 21 on December 28, then 16 on December 29 and 15 on December 30.
But NR said that 8,000 more trains will run over the festive period than in the Christmas/new year 2008/09 period and that there will be 33% fewer replacement buses.
Rail customer watchdog Passenger Focus welcomed the promise of less disruption this Christmas but said it was "regrettable" that the work affecting travel to and from South Wales was taking place over the festive period.
NR said £100 million was being spent to improve the railway over Christmas and that the "overwhelming majority of the main routes and cities remained connected by rail" over the holiday period.
The main areas affected by engineering work over the festive period include:
* BRISTOL TO NEWPORT, SOUTH WALES - December 27 to January 3 - The first phase of the £150 million Newport area improvement scheme will be completed over the Christmas break. The rail route into South Wales from Bristol and Gloucester will be closed over the Christmas/new year period, affecting services of Arriva Trains Wales, CrossCountry and First Great Western (FGW)
* SOUTHAMPTON AREA - December 21 to January 3 - Part of a £71 million project at Southampton. Train services which pass through Southampton will face disruption. This affects services run by FGW, CrossCountry, Southern and South West Trains.
* THAMESLINK UPGRADE - December 27 to January 1 - Part of the £5.5 billion Thameslink upgrade project. First Capital Connect services over Christmas will run on the Thameslink route but will not go through the central London 'core', between St Pancras International and London Bridge/Herne Hill.
* LIVERPOOL STREET STATION, LONDON - December 27 to January 3 - Part of £200 million overhead line improvement scheme. Services on National Express East Anglia services from Liverpool Street to Stratford in east London will be affected.
NR operations and customer service director Robin Gisby said: "We're doing a lot of work this year to make Britain's railway better but the overall effect on the passenger is markedly less.
"Passengers will see more trains, fewer buses and a better service this Christmas holiday period as our vital improvement work starts to use new techniques and equipment that lessens the impact on train services. This will be the model for the years ahead as we invest heavily to build a bigger, better railway."
Passenger Focus chief executive Anthony Smith said: "Although investment in the railway is important, it is vital engineering works finish on time and passengers are properly informed so that they can consider their travel arrangements.
"Where bus replacement services are required they must be made a simple and comfortable to use. Furthermore, passengers should not have to pay the same price as a rail journey for travelling on a bus."
He went on: "Passengers planning to travel between South Wales and England over the Christmas break will be shuttled onto a bus replacement service. Regrettably, it appears this work could not be planned to avoid this major disruption."
Michael Roberts, the chief executive of the Association of Train Operating Companies, said: "The vast majority of people travelling by train will be unaffected by improvement work over the Christmas and new year period.
"On the small number of routes that will be affected, train companies have been focusing all their efforts on letting passengers know about any changes to their normal journey."Reuse content