Paris is preparing to have a car-free day on September 27 as a symbol of support for sustainable transportation and increased climate action in advance of the climate talks to be held in Paris this December. In fact, many other cities including Brussels, Stockholm, Lisbon, and Budapest and are also having car-free days during European Mobility Week (September 16-22), and September 22 has been named World Car-Free Day. A car-free day is such an impressive gesture – regardless of whether it has a big impact on emissions, symbolically I think it demonstrates a strong commitment to sustainability, and I think it is a great way to energize the conversation about emissions reduction.
And, all of that got me thinking about the impact of a car-free day on carbon emissions…
What if everyone in the U.S. didn’t drive for one day? Would that make a dent in our country’s CO2 emissions? Let’s take a look at the numbers…
- 254 million Approximate number of cars/light trucks registered in the U.S.
- 36.92 Approximate number of miles driven by the average U.S. car per day
- 24.1 Approximate fuel efficiency of the average U.S. car/light truck (in miles per gallon)
- 0.008887 Approximate number of metric tons CO2 emitted by one gallon of gasoline
So, when we do the math…
[(254,000,000*36.92)/24.1]/.008887=3,458,068 metric tons of CO2
So, if everyone in the U.S. stopped driving for a day, theoretically we would prevent approximately 3.5 million metric tons of CO2 emissions. Not bad!
Compared to annual net emissions (6.673 billion), that’s a relatively small amount (only about 0.5%). And, when you think about it, one day without driving still represents only 1/365th of our annual driving, so of course its impact would be marginal. But, it can’t be denied that small changes do add up in a significant way, so that reduction in emissions would be nothing to laugh at.
While reducing miles driven would be a large challenge and a day with zero driving seems completely unlikely in most of the U.S., what strikes me is that there are two drivers of automobile CO2 emissions that could very feasibly be reduced: fuel efficiency and CO2 emissions per gallon of fuel. If we were to double the fuel efficiency of the average car, we halve our CO2 emissions from cars. The Prius already achieves a fuel efficiency of 50 mpg, and the White House finalized standards in August 2012 requiring cars and light trucks have a minimum of 54.5 mpg fuel efficiency by 2025.
Additionally, companies are experimenting with cleaner fuels. While primarily used in airlines, Fulcrum BioEnergy is testing a fuel made from household trash that could reduce jet engine CO2 emissions by as much as 80%.
So, while we may be car dependent in the U.S., our cars don’t have to be significant drivers (pun intended) of pollution.