Driving to Maximize Your Fuel Economy

With careful driving techniques it's possible to significantly exceed the EPA mileage rating for any car. Source: U.S. EPA. Click on image to enlarge.

In this column I usually focus on how to save energy in our homes and businesses, but for many of us, getting around is our largest energy consumer--particularly in the summer months when we're not heating our houses. Some of us are lucky enough to have hybrid cars, and this gives us a head start in saving transportation energy. I just calculated that the 2003 Honda Civic Hybrid we own, which averages about 40 miles per gallon (mpg) year-round, has saved us about 2,800 gallons of gas over the 146,000 miles we've driven it (compared with a car getting the U.S. average of 22.5 mpg)--worth $7,000 with gasoline at $2.50 per gallon. But for those who don't have a Toyota Prius, Honda Insight, or other hybrid, there are some simple ways to significantly reduce fuel consumption. It's easy to find tips for more efficient driving, but some of the more extreme strategies have come out of the hypermiling movement. In 2006, Wayne Gerdes coined the term "hypermiling" to describe the goal of exceeding the published EPA fuel economy ratings of cars--especially hybrids. Details of this practice can be found at Gerdes's website: CleanMPG.com. Through hypermiling techniques, some hybrid car owners have been able to coax their mileage to over 100 mpg, and they compete with one another for boasting rights. Using the same techniques, drivers of conventional cars have been able to increase their fuel economy by as much as 50%--sometimes matching that of hybrid vehicles. While hypermiling has become a sort-of game for some drivers, for the rest of us the strategies they use to squeeze more miles out of a gallon of gasoline can help us save a lot of money--even if we don't go to the same extremes. Below I've listed a few of these hypermiling strategies. Look for more tips next week. 1. Slow down. A physicist will tell you that the power required to overcome aerodynamic drag (wind resistance) increases as a cube of the velocity being traveled. This is the main reason (there are others) that at higher speeds, your fuel economy drops. A September 2009 Consumer Reports blog reported the fuel economy of a 2.5-liter, 4-cylinder Toyota Camry driven at 55 mph to be 40.3 mpg, while at 65 mph the fuel economy dropped to 34.9, and driven at 75 mph it dropped to 29.8 mpg--26 percent lower than at 55 mph. Our Honda has a digital fuel economy read-out, so I can see this effect very directly. On a trip when I'm running late to the airport and driving at 70 mph, my fuel economy may drop to 35 mpg, but on the return drive, if I keep the car to 55 (or even lower), I can get well over 50 mpg. 2. Avoid aggressive driving. Rapid (jack rabbit) starts and hard braking can reduce fuel economy by one-third, compared with more sensible driving. In his widely read 2006 article on hypermiling, Gerdes suggested that "you drive as if you do not have brakes." If you knew that your brakes weren't working, you'd leave extra space between your car and the one in front, and you'd coast to a stop for traffic lights and stop signs; these techniques will save a lot of fuel.

Hypermiling aficionados compete with one another to achieve the highest mileage. Source: CleanMPG.com.

3. Avoid cold stops--safely. Your car uses a lot more fuel when starting from a complete stop so, when you have a choice, avoid coming totally to rest. When approaching a traffic light that's red, for example, slow down so that you're still moving when it turns green. Don't violate laws or put yourself (or others) at risk in doing this, however. This isn't a suggestion to roll through stop signs, or slow down so much when approaching a light that the driver behind you will try to unsafely pass you. 4. Remove roof racks when not needed. Anything that increases aerodynamic drag will reduce your fuel economy. I do a lot of paddling, for example, but I always take the canoe racks off our car when we don't need them. Even a flag flying from your radio antenna will lower your fuel economy by as much as a mile per gallon--which is why it was ironic when, after 9/11, so many drivers sported large American flags on their antennas to demonstrate their patriotism. (By flying those flags as they cruised down the highway, they used more gasoline, increasing our dependence on oil imported from unstable parts of the world, and indirectly at least, putting more money into the coffers of some foreign entities that may have funded the very terrorism these flag-flying patriots were protesting.) In addition to this Energy Solutions blog, Alex writes the weekly blog on BuildingGreen.com: Alex's Cool Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail--enter your e-mail address in the upper right corner of any blog page. Alex is founder of BuildingGreen, LLC and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.