Passengers going through London Waterloo are warned to prepare for major disruption once a massive project begins on Saturday.
The station, which sees an average of 270,000 journeys a day, will have 10 of its 18 platforms closed until August 28.
The work is to allow longer trains to operate on suburban routes from 2019.
There will be a significant reduction in service on South West Trains going from key commuter cities, like Woking and Guildford.
Rail chiefs have urged commuters who travel regularly through Waterloo to work from home, take a holiday, or try to adjust their journey.
First Group and Hong Kong-based group MTR are due to take over South West Trains from August 20.