GRAND CANYON NATIONAL PARK, Ariz. (AP) — Visitors headed to the Grand Canyon lately know to expect two things: breathtaking views and long waits.

Tourists are showing up in big numbers at Grand Canyon and other national parks like Zion, Yellowstone and Yosemite. The crowds are driven by good weather, cheap gas and marketing campaigns ahead of next year’s National Park Service centennial.

With the busy Labor Day weekend still ahead, the Park Service already has recorded 5 million more visitors from this time last year.

Park officials are making due with the resources they have and paying overtime to keep as many entrance gates open as possible. Visitors are encouraged to use shuttles.

The Park Service launched a campaign this year to reintroduce the parks and is giving free passes to fourth graders and their families.