Tuesday, March 26, 2019

Want to burn less gas? Try driving the speed limit.


By Craig K. Chandler
Monday, March 25, 2019

Suppose that tomorrow you decide to work from home – skipping a commute that normally results in the emission of 10 pounds of carbon dioxide. That’s what would occur if your commute burned about a half-gallon of gasoline.

This is 10 pounds of CO2 that will never be generated and emitted into the atmosphere because of your decision to work from home. Work from home one day a week for a year and you will have not added nearly 500 pounds of CO2 to the atmosphere.

Multiply choices like that one by an estimated 115 million American commuters, and the amount of CO2 not emitted into the atmosphere would be hundreds of millions of tons over the course of the next decade. Expand that a few million times across the globe, and the non-emissions increase substantially.

Making these choices are like “drops in a bucket.” Turn off the light when you leave a room: a drop in the bucket. Adjust the thermostat as you leave for work: more drops in the bucket. Buy a fuel-efficient car or hybrid/all-electric vehicle instead of a big SUV or pickup truck: potentially, lots more drops in the bucket.


Every gallon of gasoline, diesel fuel, and jet fuel we don’t burn results in about 19, 22, and 21 pounds of CO2, respectively, not emitted into the atmosphere.

Ways to cut back on gallons of fuel burned are numerous: work from home; carpool; shop online; chain our trips, combining several errands into one trip. But let’s focus first on one that has not received much attention in recent years: driving slower.


Driving 60 mph is 20-25 percent more efficient than driving 75 mph. Why? Mainly because air resistance increases exponentially with the speed of the vehicle.

Declining efficiency with increasing speed also applies to hybrid and all-electric vehicles, as they too, of course, are subject to the drag of air resistance. So, if you drive your all-electric vehicle 75 mph on the highway, you will have to re-charge the car’s battery more often than if you drive 60 mph. And frequently the electricity used to charge electric car batteries is generated from fossil fuel burning power plants.

Some might urge considering the extra time it takes to drive slower. For example, suppose you must drive 25 miles on a highway to reach your place of work. If you drive 75 mph you will arrive at work five minutes sooner than if you drive 60 mph. Is that five minutes’ worth a loss of 20-25 percent in fuel efficiency?


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