MORE than five million train journeys face disruption while Glasgow's Queen Street Station is closed for four months.
Last week, Network Rail confirmed the upper-level station would shut entirely to allow the slab track in the tunnel to be replaced.
The news came a day after plans were unveiled for a £120 million redevelopment of the station, which will also cause major disruption.
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New figures show that more than 25% of all trips involving Glasgow stations either start, end or transfer at Queen Street Station.
In 2012/13, Queen Street handled 16.45 million passenger journeys. Altogether, Glasgow's 58 stations dealt with 67.7m trips.
Central Station was the busiest, with 27.1m journeys - up from 26.6m the previous year. The Queen Street figures increased from 16.37 million in 2011/12 to almost 16.5 million, equating to an average of 1.37 million trips per month.
Seven other stations - Anniesland, Anderston, Charing Cross, Exhibition Centre, Hyndland, Mount Florida and Partick - handled more than one million trips in the past year.
Although the work is likely to take place in 2016, Network Rail has not yet decided exactly when the station will be closed.
During the work, some services from Queen Street will be diverted to Central Station putting even more pressure on one of the UK's busiest stations.
Passenger groups said the extent of the disruption and alternatives must be outlined as far in advance as possible.
Work to redevelop the station will also take place in 2016, with reduced platform capacity and restricted access until 2019.
Robert Samson, of Passenger Focus, said the work will be one of the biggest and longest closures on the UK rail network in recent years.
He said: "It is going to be very difficult to manage the number of passengers who use the station. One of the key issues is getting information to passengers in advance.
"Passengers will put up with disruption if it means improvements, but it depends on how long it lasts."
Network Rail said the exact details of the works were still to be finalised.
Business leaders and local traders have already warned of the impact on trade.