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.

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