Yellowstone National Park had nearly 445,000 visitors in May, a 15 percent increase over a year ago.

In fact, the total number of visitors counted through the end of May — nearly 594,000 — is more than 14 percent over last year’s record rate.

The National Park Service says the most striking increase in vehicle traffic was that 594 buses entered the park last month, a 48 percent increase over May 2015.

Park managers say the increased visitation is likely influenced by the park service’s centennial year, marketing and tourism promotions in Montana and Wyoming, and lower gas prices.

Glacier National Park, too, is experiencing increased visitation this year.

Glacier’s year-to-date visitor count of 268,596 is up 17.9 percent over 2015, which was the Northwest Montana park’s busiest year ever.

During May, 178,218 visitors streamed through the park’s entrances, a jump of over 32 percent from last year, which was previously the busiest May in Glacier’s history.