Remember monorail? That Jetson-era relic, one step above an amusement-park ride, zipping around airports, hotels, and, yes, amusement parks? For a brief moment in the 1960s, monorail-cars or trains running on or under a single, elevated guide rail-looked like the future of mass transit. But that bright vision was eclipsed by a surge of highway building and, more recently, the rush to build urban light-rail systems. Monorail was written off as a novelty, fine for Disneyland but hardly a serious option.

But yesterday's dreams are today's leaps forward. Thanks partly to technological improvements, partly to new recognition of the limitations of conventional rail, and especially to the grassroots activism of impatient citizens, monorail is making a comeback. Today, space-short Japan leads the world in elevated transit, with eight urban monorails. Sydney, Vancouver, and Singapore all use monorails, as do planned communities in Brazil and parks in South Korea. Now monorail boosters in several U.S. cities are vying to make their towns next on the list.