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When New York City’s transportation commissioner returned from a recent trip to California, she seemed downright jealous. There were electric scooters in Oakland. New train lines in Los Angeles. Self-driving cars in the Bay Area. She tried them all.

“It is an incredibly exciting time to be in urban transportation,” the commissioner, Polly Trottenberg, told a breakfast gathering of powerful New Yorkers, pointing to California’s progress.

Her glee signaled a noteworthy and sobering shift. Wasn’t it her city that was once the envy of the nation when it came to transportation?

Not anymore. The subways on the East Coast that allowed New York, Washington and Boston to thrive are showing their age and suffering from years of neglect, while cities on the West Coast are moving quickly to expand and improve their networks.