Officials in Grand Canyon National Park recently broke ground on a new light-rail system that will completely change transportation inside the park, cutting vehicle traffic by 80 percent. Once the system is completed, most visitors will be required to leave their cars in a lot well outside the park and enter by light-rail; once inside the park, they will get around by bike, foot, or buses powered by electricity or natural gas. The Grand Canyon has some 5 million visitors a year, and on a typical summer day at the popular South Rim of the park, more than 6,000 cars fight for 2,400 parking spots. Other national parks, including Zion and Bryce Canyon in Utah, are also embracing mass-transit plans.