MEXICO CITY _ For decades, Mexico City has been famed for two things: its sprawl and its smog.

But if Mayor Marcelo Ebrard has his way, one of the world's most populous cities also will soon be one of the most green.

Under the mayor's ambitious Green Plan, a 15-year eco-roadmap launched in late 2007, the Mexican capital will have more bike lanes than Amsterdam and more rent-a-bike stations than Paris. All new buildings will be solar-powered and once filthy...