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        Transportation is useful and often necessary. However it is also very carbon intensive, especially in the US. In 2012, the transportation sector (cars, trucks, planes, etc.) was responsible for 28% of the total US’ GHG emissions.

credit: epa.gov

        However as this EPA report points out, this number comes from a limited analysis. Transport really means you need a vehicle, fuel, and infrastructure (eg. roads, parking lots). Furthermore a full life cycle analysis includes upstream impacts (eg. what it took to manufacture a truck), direct impacts (eg. having pavement get worn down), and downstream impacts (eg. disposal of waste). Therefore the 28% figure refers to only one square (unshaded below) of the nine involved in transportation.
credit: epa.gov
        The report did address the 4 top left boxes in chapter 10. By accounting for these emissions, the emissions impact of transportation increased by a third. That means transportation is responsible for at least 37% of total US emissions (that’s more than the entire electricity sector with all its coal-burning). But what about the other five squares?
“The analysis also did not assess infrastructure lifecycle emissions or the land use impacts of transportation, such the removal of trees for highway construction, parking lots, airports, and many other types of infrastructure. Measuring the latter impacts is extremely challenging.”
“Accounting for international boundaries could significantly increase total transportation sector estimates.”
        The study ignores the carbon emissions associated with paving thousands of miles of roads and parking lots and building bridges. It also ignores some foreign impacts. So even though Americans are demanding cars and fuel from overseas, those production emissions are often attributed to other countries.
        As I’ve discussed before, switching to renewables for transportation is very challenging. The most obvious reason is that fuels like gasoline are incredibly useful, but hard to substitute. The other reasons are clear once you consider the entire transportation system of vehicle, fuel, and infrastructure. All three are only cheap because fossil fuels have been so abundant.
        The best way forward seems to be to not use fuel and not use personal vehicles. Cities should be developed to encourage walking and biking. When trips are longer, we should use the cleaner electricity generated by renewables directly. Not with plug-in cars, but with city transit, freight trains, and high-speed passenger trains. We ultimately need to build societies that don’t need thousands of miles of highways or 2000-pound metal shells for each person.