Taylor Swift's Eras tour is projected to generate over $2 billion, making it the highest-grossing concert tour in history.
Fans are warned of significant traffic delays on the M4 for the sold-out Cardiff show, with 70,000 attendees expected.
Previous concerts by other artists, such as Ed Sheeran, saw attendees caught in extensive queues, prompting advice to use public transport.
Swift's concert in Cardiff will attract fans from a broader region than typical events at the Principality Stadium.
Extra trains will be provided by Transport for Wales and GWR to accommodate the influx of fans, with more than 15,000 additional seats available.
Fans began queuing early, with some arriving as early as midnight, including international fans and those with VIP tickets.
Cardiff city center will have road closures from 12:00 BST until midnight, with heavy police presence and security measures in place.
Cassie Evans, a young cancer survivor, hopes to receive Taylor Swift's "22 hat," a tradition in her live shows, as a symbol of her recovery journey.