BATTAMBANG, Cambodia—Lim Sareub needed a ride home recently, so she did the usual thing. She went to an abandoned train station, sat down on a Dr. Seuss-like contraption just inches above the tracks, then rocketed down the rails on a train made of bamboo.

The wiggly old tracks stretched into the distance like two wet noodles. The bamboo train—just a platform the size of a bed, really—gained speed and began shuddering.

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