EPA Apps for the Environment Challenge 2011 Winner: Hootroot

Hootroot helps you navigate efficiently from point A to point B. Powered by web services from Brighter Planet, Google Maps, and HopStop, the app provides directions and carbon footprints for driving, transit, flight, and human-powered transportation options on any route. 

Data for footprint calculations comes from the EPA's US Greenhouse Gas Inventory and eGRID database, as well as from DOT, EIA, and others. As a web app, it requires no installation -- simply head to http://hootroot.com and start using the tool. Give a hoot, green your route.