Network Rail say plans for Cardiff Central will see the listed building extended "to create a bigger, better and brighter station".
Network Rail says work could start in 2019.
With passenger numbers forecast to grow significantly over the next decade and beyond, the station also needs to respond to the rising demand. The remit for the initial design work has been to integrate the historic elements of the station into a building that reflects passenger needs.
Upgrading to the signalling technology in the Cardiff area is already underway and work has also started to electrify the line from Swansea to London. Network Rail says this will also mean faster, more frequent trains across the South Wales network.
- Over 11.6 million people entered and exited Cardiff Central station in 2013
- Commuting by rail into Cardiff could increase by up to 69% in a decade