Last summer, when nearly 2 million vacationers descended on California's Yosemite National Park, the line of cars at the South Entrance was often nearly a mile (1.6 km) long. Rangers walked from car to car pacifying irritated visitors with free maps and friendly advice, but during particularly busy periods, they gave up, raised the gates and waved folks through just to keep the crowd moving.
When conservationist John Muir helped create Yosemite in 1890, he could walk for hours in the 1,200-sq.-mi. (3,100 sq km) oasis without seeing another human being. Not so today, especially since a Ken Burns documentary series on PBS in 2009 boosted the popularity of all national parks. Over 281 million people visited the parks in 2010, and while that's great for the coffers, the incursion of so many humans means that parking is difficult and the lines at concession stands can rival those at the U.S. Open. Even crime is up; the number of assaults spiked 20% last year.
In part because rising airfares will spur more domestic vacations, national-park officials are expecting 2011 to draw the biggest numbers ever 4.2 million at Yosemite alone, a 10% increase over last year. "The fact that people love their parks so much is a great thing," says David Barna, a spokesman for the National Park Service (NPS). "We just need to figure out how to accommodate everyone without impacting the experience too significantly."
The NPS is preparing for the onslaught with a series of measures, including adding shuttle buses to take visitors through the most heavily trafficked areas and requiring reservations for popular attractions. At Yosemite, it has even hired guides to optimize space in parking lots. "If visitors park themselves, [our biggest lot] holds 350 cars, but if we're helping them, we can fit 550 or 600," says Scott Gediman, a spokesman for the park. (And where will the parking guides park? In the same lots.)
In the more distant future, experts contend, parks may have to take even more drastic action, such as capping the number of daily visitors to certain areas or closing areas altogether. Bob Manning, a professor of natural resources at the University of Vermont, suggests the national parks might have to borrow some strategies from their man-made counterparts theme parks like Disneyland. "Might we see something like a FastPass at a national park? It sounds far-fetched, but 30 years ago, the idea of shuttle buses probably seemed silly too," he says.
This article originally appeared in the April 25, 2011 issue of TIME.