More platforms and longer trains for Waterloo station
Five former Eurostar platforms at London Waterloo station will be brought back into service.
The £800m redevelopment of Britain's busiest station will also extend platforms 1-4 to accommodate longer trains to Reading.
It comes after South West Trains announced the launch of a new fleet of trains with free wifi, wider doors and air conditioning.
Waterloo's peak time capacity will rise by 30%, say Network Rail.
The work programme will mean taking eight platforms out of service during August 2017, with "significant changes" to services.
During this time the five Waterloo International platforms, which shut in 2007, will reopen temporarily, before closing again for the construction of a new passenger concourse.
All 24 platforms will be open by December 2018.
"This is the biggest package of improvements for passengers travelling to and from Waterloo for decades. It will provide passengers with a better station, extra seats and new trains," said Sir Peter Hendy, the chairman of Network Rail.
"And let's face it, this is not before time. Since 1996, the numbers of passengers on routes into Waterloo have more than doubled."
- 150 new carriages to run between Waterloo and Windsor & Eton Riverside
- £2m saved in energy costs
- Longer platforms at 10 commuter stations to allow 10-car trains
- More capacity at Surbiton and Vauxhall
In January, Transport Focus' report on the South Western franchise found that only 37% of passengers travelling at peak times thought there was enough room to sit and stand.
They also complained about poor mobile phone reception across the network.