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

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

"The level of frustration, we've certainly seen an increase in that," said Kyle Patterson, Rocky Mountain National park spokeswoman. "Sometimes they take it out on each other, and sometimes they take it out on the park."

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 the flat, leaving parks to grapple with the problems without higher staffing levels.

"We love having people come to the park," said John Marciano, Zion National Park spokesman. "But our No. 1 goal, our mandate, is to preserve the park into perpetuity and to ensure our visitors have a best of kind and safe experience."

Overall visitation to national parks is on track to surpass 325 million in 2016, breaking last year's all-time high of 307 million, federal figures show. The record-breaking three-year stretch came after parks visitation ebbed and flowed between 255 million and 287 million for nearly three decades.