Transport for Wales is warning that social distancing will be impossible on rail services for Wales v New Zealand international as tens of thousands of fans head to Cardiff city centre.
The event this Saturday (5.15pm kick-off) is the first sell-out event at the Principality Stadium since before the Covid pandemic.
That means public transport and travel routes are set to be extremely busy this weekend.
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Transport for Wales say they will be running a full timetable "with additional capacity on our busiest trains and all available carriages will be in service".
However, they have warned that social distancing will not be possible on matchday services and have urged customers to take this into account before travelling.
Travellers are also being warned they must wear face coverings on public transport in Wales. Police will be at stations and anyone without an exemption refusing to wear one will be refused travel.
A spokesman told WalesOnline: "With 74,500 people at the Principality Stadium and many more thousands expected into Cardiff to watch the game in pubs and other venues, social distancing is not going to be possible on match-day services.
"We would urge customers to take this into account when choosing whether or not to travel and ask everyone using our services to be courteous to fellow passengers and our staff at all times.
"We have a number of measures in place to keep passengers safe including hand sanitiser at stations, enhanced cleaning regimes on trains and stations and queuing systems to control the flow of people into stations and onto trains.
"We would also strongly encourage those travelling shorter distances to walk, cycle or use local bus services."
For those using rail services, they are advised to allow plenty of time to get into Cardiff prior to kick-off and are advised to make their way to Cardiff Central railway station straight after their match for their return journey.
As for face coverings, which are mandatory on public transport in Wales, British Transport Police will be on hand to engage with passengers.
A TfW spokesman added: "We work closely with the British Transport Police to ensure people wear face coverings on TfW services.
"TfW staff and BTP officers will be engaging with passengers at stations and anyone refusing to wear a face covering without an exemption will be refused travel.
"We’ve also been engaging with rugby clubs to help pass on the message that it’s the law to wear face coverings on public transport to and from the match.
"Anyone who forgets to travel with a face covering should speak to TfW staff for assistance."
Customers can use TfW's Capacity Checker tool to see which services are likely to be busiest, but on matchdays all services are expected to be very busy throughout the day in south Wales.
Anyone travelling from west or east Wales into Cardiff along the mainline is advised to use larger capacity inter-city services where possible.
Visit Cardiff say there is no railway upgrade work affecting services in and out of Cardiff on Saturday, October 30.
On Sunday, October 31, the Severn Tunnel is closed for essential maintenance, so services to and from London will be diverted via Gloucester. A rail replacement bus service will be in place for passengers travelling to Bristol.
If you have any issues on the railway, you can text the British Transport Police on 61016 or call 0800 40 50 40.