I agree that there was a tremendous environmental benefit to motor vehicles replacing horses in cities - but there was not a great benefit to the tremendous increase in mobility that the automobile brought, as Mr. Staley seems to think.
Of planners and horses
Once again, I've had the audacity to suggest that cars are not evil incarnate, especially considering what they replaced. My most recent blog post on Planetizen.com draws on an excellent article in the transportation journal Access, that suggests that horses were terrible for the environment and cars were, at least incrementally, better all the way around. The post and response from various professional planners (some of whom make sane and lucid comments) can be found here. In closing, I'll quote from one of the responses: