The Firefly Music Festival opened Friday on a wooded tract near Dover Downs speedway.
Department of Transportation officials said heavy traffic will likely continue throughout much of the day.
They're urging festival goers driving south on Route 1 to take Exit 95, Bay Road, turn right at the first signal, which is Bay Road, and continue on Bay Road to northbound Route 13 and Leipsic Road.
Gov. Jack Markell planned to join festival director Greg Bostrom and Dover Motorsports CEO Denis McGlynn at a news conference Friday celebrating the event.
This year's lineup the Red Hot Chili Peppers, Vampire Weekend, the Avett Brothers, Foster the People and Tom Petty and the Heartbreakers.