Extra train services and road closures will be in place in Cardiff to accommodate the sell-out crowd attending Wales' Six Nations showdown with England.
Wales will be hosting rivals England at the Principality Stadium on Saturday in what could be a decider for the championship - both sides have won their first two matches in this year's tournament.
Victory for Wales would see them make it 12 successive wins, breaking their record of 11 games undefeated set between 1907 and 1910.
England have won the last five Six Nations encounters against Wales, including two in Cardiff.
The WRU are urging fan to get to the stadium early despite saying security checks are now running smoother.
There will be a full city centre road closure between 1.15pm and 7.45pm, with kick off taking place at 4.45pm.
GRW said will run 22 trains to help fans get home after the match, but have warned that they may have to queue for trains immediately after the game.
Services before the game are expected to be extremely busy, particularly around the Cardiff area.
Following the game, there will be eight Intercity Express Train services from Cardiff to Swansea, providing over 5,000 seats; and will also run 14 train services towards Bristol, providing another 5,000 seats.
However, Transport for Wales said there will be limited capacity on local Cardiff and Valleys routes and are advising fans to not to wait until the last train to go home.
Cardiff Queen Street will close at 18.00 while a post-match queue system will be in place at Cardiff Central station - which could mean queues lasting up to ninety minutes.
Buses will be diverted out of the central city bus stops. Buses displaced from stops within the closure will relocate to either Churchill Way for the east and Greyfriars Road for the north or Tudor Street for the West.
Those not attending the match are being asked to avoid travelling to and from Cardiff on Saturday.