Trim The Fat Tuesday: The Speed Limit

I drive a looooong way to work: 41 miles each way. It takes over an hour each way. I know it's totally insane, but I like where I live, and I like my job. Still, it's an expensive commute. We all know that driving fast kills your gas mileage, so I thought I'd see how much money I could save each month by driving a little more slowly.

Stick to a personal speed limit of 70 mph.

To alleviate some of the pain, we bought a shiny new car last summer--first one ever for us! It's a Prius-C, which is like the cute little sister in the Prius family. Because it's extra small, it gets absolutely kick-ass mileage. (It also has fun gadgets like a touch-screen GPS and bluetooth that streams music from my phone and all kinds of fun built-in apps.)


One of the great things about this car is that it offers a lot of feedback on your driving to try to get you to do it more efficiently to save gas. For example, you can enter the gas price when you fill up, and the car will calculate how much you spent on the mileage counter for your trip. It also helps you drive using the least amount of gas possible by showing when you're in EV mode (all electric), when you're in the green "eco-mode," and when you're in the red burning up all kinds of gas. If you keep an eye on it, it will change the way you drive and make hypermiling much more natural.

 

(Apologies for the dusty dashboard display. Guess I should get on that.)

With such great tool staring me in the face every day, I thought I'd try an experiment to see if I could get better mileage by setting a personal speed limit for myself. First, I set my trip counter to measure a regular week of driving, so I would have a baseline for comparison. Here are the stats:

Regular week
479.8 total miles
48.3 mpg
$33.65 spent at $3.39 per gallon for gas
Average speed: 31 mph
Time spent driving: 15h 23m (ouch! that's a lot of time behind the wheel!)

Then I set my cruise control on the highway and refused to drive above 70 mph for a week, here's what happened:

464.1 total miles
49.7 mpg
$31.66 spent at $3.39 per gallon for gas
Average speed: 32 mph
Time spent driving: 14 h 33 min (still a lot, but clearly driving faster doesn't get you there any faster!)

I definitely spent less and got better mileage with the speed limit, but I also drove a little bit less. To compare apples to apples, we need to take the price of gas at $3.39 per gallon and divide it my the mpg to figure out the price per mile. For the regular week, that is $3.39 / 48.3 mpg = .070, or 7 cents per mile. For the speed limit week, the math is $3.39 / 49.7 mpg = .068, or 6.8 cents per mile.

To figure out how much money I save each week with the speed limit, let's say that during an average week I drive 475 miles. During the regular week, that's 475 miles x 7 cents = $33.25. With my self-imposed speed limit, it's 475 miles x 6.8 cents = $32.30.

That's a savings of 95 cents each week. (Totally rounding that up to a dollar, btw.) It's not a ton, but I'll take it, along with some karmic brownie points for burning less fuel and helping the planet out. Maybe I'm also increasing my longevity by upping my safety factor. The mileage gets even better in the summer--usually 53-54 mpg, but winter keeps the numbers down for now.

Savings per month: $4

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