It reminded me of a fictional acquaintance years ago who had the fictional opportunity to make an investment in renewables that would take the equivalent of 20 cars off the road. But then he found out what the price tag was, and just couldn’t swallow it. However, by then he was so enamored of the idea of ‘taking cars off the road’ that he decided to just go ahead and do it – take cars off the road. So one night he drove to the local dealership in an ancient pickup truck. He totaled 20 cars. It was dark, so he wasn’t really paying attention to the cars he was vandalizing. The next day, he found out he had destroyed 20 new electric vehicles, so he really only took the equivalent of about three motor scooters and an electric bike off the road.
A ridiculous tale, for sure, but it does raise a question: when you see a press release touting a renewable investment or efficiency project “taking the equivalent of x cars off the road,” what does that mean? What kind of cars are they? How old are they? How far are they going and who’s driving them?
As it turns out, there IS an answer to all of those questions (well, except for the last one). The EPA actually has a definition for avoided vehicles (currently stuck at 2010 vintage), and it assumes the following:
Passenger vehicles are defined as 2-axle 4-tire vehicles, including passenger cars, vans, pickup trucks, and sport/utility vehicles. Said vehicles have a 2010 combined weighted average fuel economy of 21.5 miles per gallon, and travel an average 11,493 miles a year.
The 2010 ratio of CO2 emissions to total greenhouse gas emissions (including CO2, methane, and nitrous oxide, all expressed as carbon dioxide equivalents) for passenger vehicles is 0.985 (EPA 2012).
The amount of CO2 emitted per gallon of gasoline is 8.92 × 10-3 metric tons, so to calculate annual greenhouse gas emissions per vehicle, the EPA divides the annual vehicle miles by average gas mileage to arrive at gallons consumed, and then multiplies by CO2 per gallon to get total CO2 emissions. These are then divided by the ratio of CO2 to total GhG emissions to arrive at the magic number: 4.8 metric tons CO2E /vehicle/year.
That’s really boring math. What will make it more fun and challenging, though, will be as we inch closer to the Obama Administration’s Fuel Economy Standards of 54.5 mpg by 2025, which will change the basis for calculations every year.
If nobody sabotages this efficiency goal, and it actually comes to pass, press releases in 2025 could be quite different. They may look something like “New State-Wide Energy Efficiency Program Will Be The Equivalent Of Taking Three Cars Off The Road.” We can only hope.
Oh, and the next time somebody announces that a program or technology takes so many thousands of cars off the road, can we make sure they are removed from the SouthEast Expressway up to Boston to ease my commute just a little?