PHOENIX—The light rail glides through downtown, disgorging commuters with a jangle of bells every 12 minutes. Just a few blocks away, Interstate 10 is backed up for miles.

“It’s so difficult to drive here every single morning, so I park my car at Mesa and I take the light rail,” said Jackie Rios, a freshman at Arizona State University’s downtown campus as she waited to board a train on her way home to suburban Chandler.

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