SALT LAKE CITY -- Visits to U.S. national parks set a record in 2016 for the third consecutive year as landmarks such Zion, Yellowstone and Rocky Mountain experienced historic levels of popularity that brought headaches stemming from crowded roads and trails and increasing visitor misbehavior.

At many parks, visitors waited an hour or more in cars to get through entrance gates and spent the day trying to outmaneuver fellow visitors for parking spots and room on popular trails. They left behind trash and sometimes, human waste.

Encountering a crowded, Disneyland-like situation when people were expecting peaceful serenity can lead to aggression and bad decisions, park officials said.

It created a good news-bad news story for park managers. They praise the increased interest but are struggling to preserve iconic mountains, slot canyons and wildlife habitat for future generations. The National Park Service budget has remained basically flat.