Sustainability as it relates to architecture is so much more than just creating a green building. Most western U.S. cities are so inundated with sprawl that even if most of the buildings within the city were sustainable people would still be almost completely dependent on the automobile (see Los Angeles, Phoenix, and Las Vegas).
This talk is centered around the urban sustainable strategies implemented by the city of Curitiba, Brazil. Like all major metropolises throughout the world Curitiba was facing limited budgets in an effort to solve urban issues relating to mass transit and pedestrian friendly environments. The city successfully created a mass transit system using express buses, which treated the buses more like a light rail (dedicated streets and quick loading and unloading stations) and less like a car (share the streets with other vehicles and be stuck in the same traffic jams).
There are other attributes that Curitiba implemented that make the city a people centric environment. When American cities start focusing the built environment on people you will most likely hear about Curitiba being cited as an inspiration.
Blue Architecture 
really good point about the transportation issue in discussing sustainable cities. that said, “green” buildings are still an excellent start. this is a really cool design that just won an award in sustainable innovation: mygreenpalette.com/projects/detail/121