Rainer Zietlow's German company Challenge4 GmbH has spent the last few years driving immense distances in a Volkswagen Caddy EcoFuel powered by compressed natural gas (CNG). In 2006 and 2007, the vehicle went all the way around the world and also did a Eurasia crossing. The current journey is Ecofuel Transamerica, which is a 15,534-mile route from Tierra del Fuego to Alaska. Zietlow began driving on January 2, 2010 in Rio Grande, Argentina at the southernmost natural gas fuel station in the world. Yesterday, it stopped in Los Angeles, about halfway through the journey to the world's northernmost natural gas fuel station in Barrow, Alaska.
According to an automatic CO2 calculator on the Ecofuel Transamerica, the can has so far traveled 19,628 miles and emitted 4959.47 kilograms of CO2. Compared to a Volkswagen Caddy with a 1.6L petrol engine going the same distance, this is 1295.15 fewer kilograms of CO2. Considering this is further than the entire trip, we're not sure what the calculator is actually counting. In any case, there are a bunch of videos from the transcontinental trip here.
[Source: Ecofuel Transamerica]