There's no question that our country's national parks are extremely popular, welcoming eager travelers looking for wide-open spaces and stunning scenery.

Many of the most popular parks had requirements or restrictions that made spur-of- the-moment trips more difficult.

To make sure that visitors get the best experience possible, some parks have been requiring guests to make advance reservations to enter the park or hike in-demand trails. If you want to avoid long waits for entry, it is recommended that you make reservations at the park.

As the fall travel season begins and summer crowds diminish, some national parks plan to eliminate or reduce reservation requirements. Some people are still requiring reservations for now.

Before booking a hotel or vacation rental near a national park, make sure you check the park's latest reservation rules because rules continue to evolve. To make sure your visit to one of the nation's most beautiful outdoor spaces is a smooth one, you'll want to figure out how much planning is needed.

Right now, there are some national park favorites that you need to know.

Yosemite National Park

Half Dome in Yosemite National Park. SCOTT CLARK/THE POINTS GUY

During peak times, from 6 a.m. to 4 p.m., advance reservations will not be required.

You have to make advance reservations for the park before Sept. 30. Even if you are only going to drive through the park, you need to make reservations. Those with reservations to stay at campgrounds or other lodging within the park won't have to make park-entry reservations.

The current peak times reservation rule does not apply to those with wilderness permits or permits for hiking to Half Dome.

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Glacier National Park. HAIZAN ZHENG/GETTY IMAGES

Glacier National Park

The Going-to-the-Sun Road is accessible from the West Entrance, St. Mary Entrance and the new Camas Entrance. The goal of the summer reservation ticketing system was to help manage traffic in the park.

Delicate Arch in Arches National Park. MARK BRODKIN/GETTY IMAGES

Arches National Park

Visitors to Arches National Park in Utah are required to reserve an admission pass through the park's timed-entry ticketing system. The park has more than 2,000 natural red rock structures accessed with limited roads and a timed entry system to manage traffic. Three months in advance, timed tickets can be purchased at recreation.gov.

A limited number of tickets are available a day before the event. If you're planning on going to Arches in September, be sure to grab one of those tickets as soon as they're available because they sell out quickly.

There is a guide to the 'Mighty Five' in Utah.

The Watchman in Zion National Park. JUSTIN REZNICK/GETTY IMAGES

Zion National Park

Zion National Park in Utah uses a lottery process to manage access to its hiking trail. Zion has stopped using tickets for the park's shuttle service, and there is no requirement for reservations to enter the park.

Permits are required for canyoneering, hiking, and camping in order to avoid overcrowding and to ensure a better experience for visitors.

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Shenandoah National Park. NATIONAL PARK SERVICE

Shenandoah National Park

You might need to plan ahead if you want to spend the night at the park.

Reservations are required for one of the park's campgrounds and the system is open six months in advance. You should secure your place as soon as possible because slots for weekends and holidays are quickly taken up. There's no need to change your fall foliage trip plan if you have some flexibility.

The Old Rag Mountain area requires advance- purchase day-use tickets. The tickets are released every 30 days and five days before the hike.

Every traveler should visit at least 20 national parks.

Elk at play in Rocky Mountain National Park’s lush meadows. MELANIE HAIKEN/THE POINTS GUY

Rocky Mountain National Park

The temporary timed-entry system in the park will remain in effect until October 10. Reservations can be made for the Bear Lake Road Corridor of the park, or for the rest of the park.

There is a reservation requirement from 5 a.m. to 6 p.m. for the corridor and from 9 a.m. to 3 p.m. for the rest of the park. If you already have a reservation for a service, you don't need a permit.

Acadia National Park. DERMOT CONLAN/GETTY IMAGES

Acadia National Park

Reservations are required to drive to the top of Cadillac Mountain for its inspiring coastal views, though travelers don't need to worry about timed entry slots. The sunrise from the mountain is considered to be one of the best in the world. It is possible to reserve a vehicle up to 90 days in advance. Two days before the event.

Haleakala National Park.

Haleakala National Park. ED FREEMAN/GETTY IMAGES

It is a once-in-a- lifetime experience to see the sun rise over Haleakala National Park. Reservations are required for every vehicle entering the park between 3 a.m. and 7 a.m. regardless of the season.

Reservations can be made online 60 days in advance. 48 hours in advance, additional slots are released. Three historic wilderness cabins are available for those who can't get enough of the volcanic landscape.

A month-by-month guide to the best national parks in the world.

A black bear cub in Great Smoky Mountains National Park. KEN CANNING/GETTY IMAGES

Great Smoky Mountains National Park

You can enter the park whenever you please, but you have to make reservations for all the campgrounds. The system is open for reservations for most campgrounds up to a year in advance, with the exception of the front country campgrounds and horse camps, which are only available six months in advance. Permits and reservations are required for overnight stays in the wilderness.

It's a popular time of the year to visit Great Smoky Mountains National Park, with nice leaf-peeping opportunities, so securing campground reservations on weekends may be a challenge.

Bill Fink reports additional information.