Cadillac Mountain in Maine’s Acadia National Park is among the country’s premier spots to view a sunrise.

For half the year, visitors to the 1,530-foot peak — the tallest within 25 miles of the entire U.S. East Coast — are the first in the country to see daylight, watching as the sun’s rays gradually illuminate Frenchman Bay and its many islands in brilliant blues and purples.

That is, if they can find parking.

Until recently, it wasn’t unusual to see 500 cars vie for 150 parking spaces, according to park superintendent Kevin Schneider.

Park officials implemented a reservation system this year to cut congestion. Reservations cost $6 per vehicle and must be bought online in advance.

Elsewhere — Yosemite, Glacier, Haleakalā and Rocky Mountain National Parks, as well as the Muir Woods National Monument — are also using advance reservations to access the whole park or popular attractions. Zion National Park in Utah is weighing the same next year for its Angels Landing hike, which sometimes sees visitors wait hours to access the trailhead.

Other heavily trafficked parks will likely take similar measures in coming years if visitor trends continue, according to officials and travel experts.

Travelers may have difficulty claiming one of the limited spots ahead of time, or are turned away if unaware of the requirement before arrival.

“They’ve traveled thousands of miles, made tens of thousands of dollars in hotel and airfare and rental car reservations, only to see their vacation ruined because they can’t get that $2 ticket to see Glacier National Park,” Kevin Gartland, executive director of the Chamber of Commerce in Whitefish, Montana, said at a recent Senate hearing on park overcrowding.

Eager to travel and get outdoors after months of confinement, Americans have traveled to some parks in record numbers this year. Vacationers may also still be wary of traveling to destinations outside U.S. borders, or may not be able to due to local restrictions.

July was Yellowstone’s busiest month in park history — monthly visitors had never exceeded 1 million to the first U.S. national park, which has the highest concentration of thermal features like geysers, hot springs, mudpots and steam vents in the world.

“Increases to Yellowstone’s visitation have accelerated rapidly over the past 12 months and we continue to be on pace to set record numbers for 2021,” according to park superintendent Cam Sholly.

Nearby Grand Teton National Park had its busiest-ever June, with a 20% increase in visitors over 2019. Visits to Zion are up 18% in 2021 through July relative to 2019, according to federal data. Likewise in Great Smoky Mountains National Park, the most trafficked in the system, where tourism is up over 7% this year versus 2019.

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These record numbers in some parks reflects a longer-term trend. Visits to Glacier and Yellowstone, for example, have doubled since 1980. National park visitation was about 20% greater in 2019 than in 2013.

There’s a “tension and a paradox” in this dynamic, according to Sen. Angus King, I-Maine, who chairs the Senate Subcommittee on National Parks.

On one hand, it’s good that Americans are visiting public lands in record numbers. But overcrowding has led to more litter, vandalism and traffic — stressing the park’s natural resources and wildlife and negatively impacting visitor experiences.

“We can accidentally love our parks to death,” King said at a Senate hearing in July.

Reservations are among the many methods parks are weighing to address congestion. Their details and restrictions vary from place to place.

For example, Glacier, in northwest Montana, is only using vehicle reservations for its Going-the-Sun Road, a scenic drive that cuts through the center of the park and is one of its main attractions. The tickets cover entry for seven days from the date a visitor selects. (They cost $2 in addition to the typical park-entry pass.)

As with other parks, spots are limited and may sell out quickly. About 75% of the reservations become available up to 60 days in advance, and the remaining 25% just two days ahead.

By contrast, Rocky Mountain National Park in northern Colorado is using a timed-entry reservation. Visitors must enter the park within their chosen two-hour time window.

In Yosemite, $2 reservations to enter to the park are valid for three consecutive days. However, the system may not be permanent — park officials said this year that the “temporary” system, which took effect in May, would help manage visitor levels to reduce Covid-19 related health risks.

Some travel experts expect parks to keep the systems in place even when the pandemic is no longer a threat.

“It was only a matter of time,” according to Kasey Morrissey, the president of Austin Adventures, a company based in Billings, Montana, that guides national park tours. “It’s not like Covid was going to be the only factor that brought that on.

“The parks are getting very, very busy.”

It’s unlikely that all — or even most — parks will adopt such systems, though.

For one, not all of them have seen a surge in traffic. Half of all recreation visits occur in the top 23 most visited parks, with “significant congestion” concentrated in the top 12 to 15, according to Michael Reynolds, a regional director at the National Park Service.

While parks like Glacier, Zion and Yosemite have limited parking in relatively small canyons or valleys, those with different geography and road systems may be able to better absorb higher traffic, Morrissey said.

And parks are exploring options beyond ticketed entries to cut congestion.

For example, Yellowstone, which doesn’t require a reservation, is exploring the feasibility of a shuttle system between Old Faithful and Midway Geyser Basin. It launched a pilot program this summer that uses free, automated shuttles to help transport people around its Canyon Village area. Visitors can book a larger number of campsites six months ahead instead of upon arrival.

Timed reservations aren’t a policy to expect anytime soon in Yellowstone, according to park spokeswoman Linda Veress.

“But it’s well within the realm of possibility in the future,” she said.  

While it may be “crushing” for would-be tourists who can’t secure a reservation, the systems improve experiences for those able to get them, Morrissey said.

And there are creative alternatives, she said.

For example, Acadia visitors can hike, bike or taxi to the top of Cadillac Mountain without a permit. Glacier and Rocky Mountain parks waive the requirement for tourists who have a “service reservation” like overnight lodging or a tour inside the park. (The waiver only applies to that day, though.)

Motorists can also drive into parks before or after their entrance booths are staffed for the day. (At Glacier, that would be before 6 a.m. or after 5 p.m., for example.)

“There are certain ways around it if you can be a little crafty,” Morrissey said.