A statement on ATW website reads:
Following discussions with Cardiff City Football Club, the British Transport Police, South Wales Police and the Welsh Government, there will be no trains calling at or departing from Ninian Park Station for Cardiff City’s home fixtures this season.
This will start from 17th August when Cardiff City will play against Brighton. Services will be suspended for 3 hours either side of kick off times and passengers are advised to use Grangetown station instead. Trains will call at all other City Line stations (Waun-gron Park, Fairwater, Danescourt and Radyr) as per the timetable.
Commenting on the changes, Peter Northcott Head of Stations said: ‘We believe that encouraging the use of Grangetown station will better suit the needs of passengers as the station benefits from more frequent services and wider platforms and will provide passengers with a more pleasant and safer journey experience to and from the match.’
Grangetown station, they claim, is just a 10 minute walk from CCS. I would say 10 mins at a good pace, 15 at normal pace and that's to the Ninian Park Gates behind the Ninian Stand. Those wanting to access the Family Stand would then have to walk around the stadium to get to the turnstiles, so a parent taking their kids might find themselves with a 30 minute or more trek to get into the ground after getting off the train at Grangetown station.
I can appreciate the safety issue after a match. I've experienced the crush to get onto the small trains they use on the City Line. But before the game the trains tend to be well used but not over-crowded. Let the fans get to the stadium as easily as possible. Put safety measures in for after the match, not before.