National Parks are often known for sweeping vistas and distinctive natural beauty. One thing more of them are becoming known for? Traffic and congestion.

Rocky Mountain National Park has experienced sharp upticks in visitors in recent years. While more visitation is generally seen as a good thing, it also can cause problems.

On a winter weekend after the New Year, cars circled parking lots along Bear Lake road like vultures, looking for a space. The parking lots tend to fill fairly early in the morning. Park spokeswoman Kyle Patterson points out that winter weekdays are "relatively quiet. But weekends are a whole other story."

In summer and early fall, visitors to trails off the popular Bear Lake Road can take a shuttle, easing some of the parking pressure. That ends in October, though, so "once the parking lots are full then that's the capacity for that trail system in the winter," said Patterson.

Trail access options in the park are more limited in winter, since Trail Ridge Road is closed, concentrating visitors at lower elevation trail systems. As more and more people move to the Front Range, that means the park is drawing more local visitors in all seasons, including winter.

Bathrooms are another issue exacerbated by high visitor numbers -- particularly in the winter. Vault toilets at high elevations can’t be pumped in wintertime, because their contents freeze. So the park keeps some of them closed. They open new ones after others fill.

The closures aren’t honored by all visitors.

At Bierstadt Lake, urine was visible in several patches of snow outside a closed bathroom, and trash had been left as well. Summer or winter, Patterson said human waste is an ongoing challenge for the alpine park. She encouraged visitors to drive to find an open bathroom in winter time.

Rocky Mountain’s challenges are not unique. It hit a record-breaking 4.15 million visitors in 2015. Several other western parks also surpassed visitor records. Among these were Yellowstone National Park, Grand Canyon and Zion National Park. That trend is expected to continue, particularly with 2016 as the centennial anniversary of the Park Service and gas prices staying low.

In Yellowstone and Grand Teton National Parks, heavy visitation is straining park resources and budgets. Traffic jams have become common on park roads and popular trails are being damaged by heavy use. According to a report by Wyofile, when adjusted for inflation, Grand Teton’s budget is down 9 percent since 2009 and the staff is 18 percent smaller since 2010.

In Zion, another popular park, officials expanded shuttle service when visitors could not find parking.

There are no plans to do that yet at Rocky Mountain National Park, despite the busy winter weekends. The surge in visitors is pretty new, said park spokeswoman Patterson.

"It’s too soon to elaborate or even really specify some of the strategies that we are looking at," she said.

The park lists managing more day use visitors as just one of its top three challenges; climate change and remaining relevant in the 21st century round out the list.