With huge crowds expected to make their way to Stradbally Hall, Co Laois, for this weekend's Electric Picnic, festival-goers are advised to travel early and allow plenty of time.
Although the first acts do not appear on the main stage until around 6pm on Friday, the campsite and parking facilities will be open from 9am.
"Long delays are likely on the key routes approaching Stradbally on Friday, Saturday and Sunday", says AA Roadwatch Controller Nicola Hudson.
Traffic is expected to be particularly heavy on the main N7/M7 southbound from Kildare and Dublin and the N7 from Limerick and Roscrea.
The N8 will be heavy northbound from Cork, with Fermoy and Abbeyleix expecting the heaviest congestion.
Those travelling from Waterford are reminded not to use the N9 through Thomastown where roadworks are in operation; the best route is the N10 via Kilkenny.
Saturday and Sunday traffic will be equally heavy on all these routes, as GAA supporters head to Croke Park for the All-Ireland hurling final on Sunday.
Galway will meet Tipperary in the Minor Hurling Final and Cork v Kilkenny in the Senior Hurling Final.
Although car parking is free at the Electric Picnic, revellers are advised that the best way to avoid the traffic jams is to use public transport.
Bus Éireann will provide special coach services to Electric Picnic from Dublin and Galway.