Extra trains for Wales rugby and Cardiff football matches
Football and rugby fans have been assured train services in Cardiff will be at maximum capacity on Saturday.
Wales host Argentina at the Millennium Stadium in the first match of the autumn Test series with about 50,000 attending the match which started at 14:30 GMT.
Cardiff City kick-off against Hull City at 15:00 GMT before a crowd of around 20,000 at the Cardiff City Stadium.
It is not the first time both teams have been at home at the same time.
But South Wales Police chief inspector Steve Murray said it was "slightly unusual".
He added: "It is credit to the city, both venues and both sets of supporters that both games can be played at the same time.
"We worked closely with closely with Cardiff City Football Club on the design of the stadium to incorporate features that would reduce the risk of public disorder on match days and create an even better family atmosphere which has been the case season after season.
"The new seating arrangement also means fewer police officers are required in the ground, and also ensure day to day policing continues as normal in communities across south Wales.
"South Wales Police is recognised nationally and internationally for dealing with major events in Cardiff and there will be plenty of officers in the city on Saturday ensuring everyone has a safe and enjoyable day."
Arriva Trains Wales has asked passengers to allow plenty of time to catch their preferred service as seats will be allocated on a first come, first served basis.
A queuing system will be in place at Cardiff Central station after the match while Queen Street station will be closed after 15:30 GMT.
Jonathan Goode, special events & security manager for Arriva, said: "If travellers are not attending the match we would strongly advise them to travel at a different time to avoid the crowds.
"Every effort is made to provide as much additional capacity as possible for major events in Cardiff and all our available trains will be in use."
Full train times and fares information can be obtained by visiting the Arriva Trains Wales website or by calling National Rail Enquiries on 08457 48 49 50.
Cardiff council said the usual park and ride facilities would be in operation for the rugby international except that those at the Cardiff City Stadium would be unavailable because of the football match taking place.