Friday, October 14, 2011

96% of U.S. transportation powered by petroleum

With all the talk of alternative fuels, it sometimes helps to put a sense of scale on things. The growing prevalence of electric cars is one rational for basing the federal highway taxes to vehicle miles traveled rather than gas consumption (more on this in a coming post). In 20 years, some predict electric cars will make up 64% new sales, but in the near term this is not the case. Even if the experts are right and there are 3/4 million electric cars on the within five years, there are currently more than 137 million licensed passenger cars in the U.S.

This double pie chart depicts what fuels transportation in America (data from The Geography of Urban Transportation, p 278). No details like passenger miles or ton equivalents, but simply trillions of BTUs (the sum of all is 27,500). Gasoline and diesel together make up more than 3/4 of the total. Jet fuel and ship fuel are much smaller but not insubstantial shares. (I'm not sure how they count international journals; another paper I saw took all the usage for domestic trips and half for international.) Our running total is up to 96.4% thus far.

Now we get to the final 3.6% that is not derived from petroleum. By far the largest chunk of this -- 2/3 of the remainder -- is another fossil fuel: natural gas. Oh, like those dual-fuel cars and delivery trucks in those articles, you think. But no, this natural gas is burned to power pumps which push more natural gas through pipelines. (It's still transportation energy, even if there's no vehicle involved.) Another quarter of the small pie is electricity used for the same purpose. Lastly, the final sixth of the little pie, or 0.29% of all transportation energy, is used in non-petroleum vehicles that actually move, like we normally think of for transportation. Of this, almost nine-tenths is electricity for subways, commuter railroads, the electrified portions of Amtrak, and a couple electric trolley buses. The rest is for natural gas buses. For perspective, this total of .29% is less than the gasoline used by recreational boats.

What about the electric cars? Well, the table only goes down to the tenth of a trillion BTUs, and the electric cars just get lost in the rounding. The other news-maker, methanol, is similarly zero. Interestingly, this doesn't imply that biofuel is insignificant. The gasoline fraction includes Gasohol, or 10% ethanol. From an FHA report, it seems that 13% of all gasoline sales are from Gasohol [Table 8 ÷ (Table 2 Sum × 365)]. This means that ethanol usage accounts for three times the energy as all other non-petroleum sources for vehicles (not counting the pipelines).