Having people fly in to Aspen from around the country for vacation is never going to be the most ecologically sound practice, but it's worth mentioning that the city seems to have a very forward-thinking set of transportation policies. For one thing, the town is walkable with sidewalks, reasonable traffic lights, and there seems to be some effort to make parking facilities relatively unobtrusive. On top of that, the Roaring Fork Transportation Authority runs an extensive and reasonable frequent bus network and there's lots of people (myself included) getting around on bikes.
Now of course being a ridiculously wealthy community has got to be helpful in terms of putting together a high-quality bus network in a somewhat unlikely situation. But by the same token there are very few countries that are as rich as the United States of America so we ought to be able to afford to construct one of the world's best comprehensive multi-modal transportation networks.