Honking cars emit foul black clouds, skyscrapers blot out the sun, litter lines the gutters and healthy green space can be hard to come by. But in many of America's biggest cities, these negative traits are being eclipsed by clean, efficient public transit, bike-friendly infrastructure, multiplying trees, reliance on renewable energy and a fierce pride in locally-produced products. Slashing greenhouse gas emissions and coming close to zero waste is no easy feat for a metropolis with a population of at least 250,000, but these 10 cities - from Boston to San Francisco - prove that sustainability is possible on the largest of scales, in good economic times and bad.
10. Boston, Massachusetts
Representing the entire East Coast in impressive renewable energy stats, Boston boosted its solar power with the Solar Boston program and 
counts wind among its top three sources of electricity, with a turbine on city hall and more slated for several public schools. Other big plans include turning fall leaves and other yard clippings into power and fertilizer with a new biogas facility, and using recycled trash to power homes. For those residents who don't rely exclusively on the nation's most utilized public transportation systems, taxis will soon be another green option as they're all required to go hybrid by 2015. New bike lanes and 250 bike racks have increased Boston's pedal power, and the city saves a whopping $400,000 a year thanks to LED traffic lights.
