Our personal vehicles may have made it possible for most Americans to travel widely, but there are definite tradeoffs. We're all familiar with the negative impacts of too many cars, SUVs, and RVs on the environment—and being caught in a traffic jam or spending a big chunk of your vacation looking for a parking place doesn't add to the enjoyment of a park visit.

Shuttle bus systems are growing in popularity as one solution to those problems, so for your convenience, the Traveler is providing the following overview of those systems at some popular NPS sites around the country.

Check the following links for each park for details, including the season of operation, and be aware that even though most of these systems are free, payment of the usual park entrance fee is still required to enter the respective parks. That's not unreasonable—those entrance fees help fund many of these systems.

If you've visited Rocky Mountain National Park and the gateway community of Estes Park, Colorado during the summer, you know that traffic can be a challenge at time. A nicely integrated shuttle bus system which joins Estes Park with some key stops in the park went into operation last weekend, and it can make visits to the area a lot more pleasant for the rest of the summer.

Rocky Mountain's shuttle system includes two routes which provide access to Bear Lake, other trailheads, the Moraine Park Visitor Center, and Moraine Park and Glacier Basin Campgrounds. A separate express route known as the hiker shuttle runs from the Town of Estes Park Visitor Center to the park's Beaver Meadows Visitor Center and then into the park, where it connects with the two park routes. The Town of Estes Park “Visitor Shuttle” will operate on three routes daily through Labor Day, and on weekends through September.

Grand Canyon National Park operates an excellent free shuttle system with five separate routes on the South Rim. The routes interconnect, but do not overlap, and all buses are equipped with bicycle racks, making it possible for visitors to bike one way and ride the shuttle the other. The Tusayan Route provides "park & ride" shuttle bus service between the gateway community of Tusayan, seven miles south of the South Rim Village, and the park.

One of the earliest entries in the park shuttle business was Yosemite National Park The park's free system includes service in Yosemite Valley as well as to outlying areas such as Wawona and the Mariposa Grove of Giant Sequoias and Tuolumne Meadows. For a fee, separate bus service and tours are available to Glacier Point, various trailheads on the Tioga Road, and neighboring communities.

Two free shuttle routes are available at Sequoia-Kings Canyon National Park (California). Stops include Wuksachi Lodge, Lodgepole Visitor Center, the Sherman Tree, Giant Forest Museum, the Moro Rock staircase, then over to sequoia-ringed Crescent Meadow. A separate for-fee service runs from the City of Visalia, through Three Rivers, and up to the Giant Forest Museum, where you can transfer to the two park routes.

At Zion National Park (Utah), the Springdale Shuttle stops at six locations in the gateway community of Springdale, and the Zion Canyon Shuttle loop stops at eight locations in the park. The transfer between loops is made at the Zion Canyon Visitor Center and the system is free.

Bryce Canyon National Park (Utah) encourages (but doesn't require) visitors who are not staying overnight in the park to park outside the park entrance and use the free shuttle, which serves key stops in the park. Bryce Canyon also offers a free daily guided tour to Rainbow Point, which takes four hours and covers 40 miles with stops along many of the park’s scenic viewpoints. Reservations are required and can be made up to 24 hours in advance. Details are available on the park website.

A combination of free and for-fee bus service is available at Denali National Park (Alaska). The free entrance area shuttles serve what the name implies; for a fee you can reserve a seat on the concessioner-operated shuttle system, which serves destinations along the entire 91-mile length of the road into the park. This is the only way to reach the interior during most of the year; for an additional fee, an interpretive tour bus will provide a more formal narrated experience during the trip.

Glacier National Park's free shuttle service began in 2007 as a way to reduce traffic on the Going-to-the-Sun Road during the multi-year rehabilitation project of that iconic scenic highway. The system connects the east and west sides of the park over that route, and I'd highly recommend it as an alternative to driving your own vehicle.

Here's an offer that sounds hard to beat: Mount Rainier National Park (Washington) is offering a free weekend shuttle to Paradise. Visitors have the option to begin outside the park in Ashford, Washington or inside the park at Longmire and Cougar Rock. Due to construction in the Paradise area, parking is limited and traffic moves slowly, so those who choose to drive their own vehicle instead of the taking the shuttle may feel their intended trip to Paradise ended up in that opposite destination.

Shuttle bus options aren't limited to western parks.

One of the most comprehensive systems is found at Acadia National Park (Maine), where Island Explorer buses provide service between park destinations, local communities, and the Bar Harbor-Hancock County Regional Airport. Regularly scheduled buses stop at specific destinations in the park—including campgrounds, carriage road entrances, and many trailheads. You can also flag down buses along their route; drivers will pick up passengers anywhere it is safe to stop.

The free Historic Triangle Shuttle connects two separate sites in Virginia's Colonial National Historical Park—Jamestown and Yorktown Battlefield—with the third side of the Historic Triangle, Williamsburg. The two routes of the Historic Triangle Shuttle depart at 30 minute intervals from the Colonial Williamsburg Visitor Center, one traveling along the Colonial Parkway to Jamestown, the other following the Parkway to Yorktown. After arriving at Jamestown and Yorktown, visitors use additional free shuttle services to the various attractions at those two destinations.

One of the newest entries in the park shuttle world is Valley Forge National Historical Park, which is "experimenting with a free shuttle around the park." The Revolutionary Shuttle runs at 15 to 20-minute intervals throughout the day.

Private companies also offer a variety of additional for-fee tours and shuttle services in parks, as well as transportation between parks and nearby communities. Check individual park sites on the NPS website for the latest ways to let someone else do the driving, while you enjoy the scenery.