I was recently presented with an opportunity to run a little gas mileage experiment. I’ve done this in the past when I investigated the degree to which I could improve my gas mileage by altering my driving habits around town. Interestingly, I was able to increase my mileage by 15% in return for a few minor driving tweaks.
This time, I had to make a 350 mile roundtrip on the interstate. As such, I decided to drive “normally” on the way out, and to go out of my way to keep my speed in check on the way back. I filled my tank at the beginning, at the turnaround point, and at the end. Thus, I was able to calculate my mileage for each leg. For background, I have a 2005 Honda CR-V that’s supposed to get 23 city mpg and 29 highway mpg.
The impact of slowing down
As noted above, I drove “normally” on the way out of town. For me, this meant running at roughly 75 mph. In order to keep things as accurate as possible, I decided to use the cruise control to hold my speed steady. While I realize that I could’ve done a good bit better mileage-wise if I had controlled my speed manually (especially on hills), I wanted this to be an apples-to-apples comparison. Upon arriving at my destination, I learned that my outbound mileage was 25 mpg.
On the way back, I decided to ratchetthe cruise control down to 65 mph and hang out in the slow lane with the trucks. At the end of the trip, I was surprised to learn that I had achieved 32 mpg – that’s a 28% improvement! To be fair, I was driving into a bit of a headwind on the way out, and had the wind at my back on my return. Then again, it was considerably warmer on my return trip, so I had to turn on the A/C to stay cool.
While I fully expected to see an improvement, I was a bit surprised by how much of an impact slowing down had on my mileage. Of course, that 28% improvement was based on a relatively small amount of data (i.e., one roundtrip of 175 miles each way), so it might not be entirely accurate. Nonetheless, speed obviously has a pretty major impact on highway mileage.
Is slowing down worth the trouble?
Sure, slowing down saves gas. But in an economic sense, was it worth it? Let’s take a look at the numbers… For simplicity, I’ll base my calculations on a 100 mile trip and $4/gallon gas — you can easily extrapolate from there.
At 75 mph… 100 miles would take 1:20, and would consume 4 gallons of gas.
At 65 mph… 100 miles would take 1:32, and would consume 3.125 gallons of gas.
So… I’d spend an extra 12 minutes on the road, but would save 0.875 gallons of gas at an estimated cost of $3.50. Extrapolating this out to an hourly rate, I could “earn” $17.50 per hour (tax free!) of extra driving, not to mention the environmental benefits of burning less fuel. Not bad considering I was relaxing and listening to podcasts the entire time.
While your mileage may (quite literally!) vary depending on your vehicle of choice, driving style, etc., the bottom line here is that you can definitely save a few bucks (and be a bit greener) by slowing down.