By now, you may have forgotten that Portland was ever crowned the Miss Universe of Sustainability, and have started packing up your bicycles and solar panels for the big move to Syracuse or Tampa.

OK, maybe you're not thinking of uprooting yourself and your family. More likely, you're evaluating your own city to figure out what green things it's got going for it, where it lags behind, and how you can make a difference where you live. Who knew affordable housing was a key to sustainability, or that vehicle-miles traveled matters as much as the number of smog particles lingering in the air?

One thing we know from the experts: the biggest barrier to sustainability is on four wheels. "When you add up all the numbers, sustainability comes down to the transportation sector," says SustainLane's James Elsen. "It's the darn car thing."

The more you can walk or ride your bike, hop on the bus, or duck into the subway, the greener your lifestyle will be. Increasingly, cities are realizing that it makes sense to offer more public transportation options to residents -- and more jobs and housing near that transit. But even those cities with fantastic public transit can rate low on the sustainability meter; tried finding affordable housing in New York City lately? How about all those abandoned homes in Cleveland, with its own award-winning public transit system?

Even when a city invokes sprawl-reversing strategies, there can be fallout: the more attractive inner-city life becomes, the more expensive it gets. Unless they integrate affordable housing strategies into their plans, as Cleveland's doing with its EcoVillage project, cities can become victims of their own success; as we learned earlier this week, most of the infill projects in Phoenix have been high-rises geared toward high-income, seasonal dwellers. A number of cities have implemented green public- or low-income housing strategies, or created individual green projects. But even then, a dearth of middle-class housing options might persist.

Clearly, there's work to be done, and an integrated approach -- working on green jobs in conjunction with air quality and parkland, adding infill housing and affordable homes, too -- is the best approach. It's not a formula that every city has figured out. But if the stories we've run this week are any indication, plenty of places are trying. Red cities are beginning to go green, sprawling places are getting more sustainable, and metropolises are choosing hope. And frankly, we find hope in that.

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