How to Save 20% on Gasoline

Recently, I realized that the fuel mileage I was obtaining in my 2005 Corolla (manual transmission) was not what it should be. I was getting around 32MPG, and could go roughly 330 miles per refueling stop. I knew that the car was much more capable, as I'd seen mileage as high as 37MPG in the past.

I decided to run an experiment. With a few changes to my driving style, I found myself getting over 40MPG! To put this in perspective, that's like going to the gas pump, filling up your tank, and paying 20% less! (for eaxmple: $2.47 per gallon versus $3.09 per gallon prior to changing driving styles). My commute to and from work takes about 5 minutes longer than previous, yet it is more consistent (no stop-and-go traffic). So, how did I do this?

Brakes: Your Enemy
Efficiency is defined as the ratio of useful output energy divided by the input energy. Differences between input energy (gasoline consumed) and output energy (proportional to miles driven) are caused by losses of energy due to heat, wind resistance, and mechanical resistance. There's not much you can do about wind and mechanical resistance, other than removing your roofrack, etc. However, you can dramatically reduce losses due to heat caused by braking.

Using the Brakes
Every time you press the brakes, you are generating heat, thereby wasting the energy you provided (gasoline) to your car to achieve the speed you were traveling at. Another way to think about this is to compare your decrease in speed while braking with the required use of the accelerator to achieve an equivalent gain in speed. This technique is simple: Don't use the brakes unless you need to, OR, AVOID SITUATIONS WHERE BRAKING IS NECESSARY. This means you should avoid tailgating. You should also try to preemptively anticipate red lights, slowing traffic ahead, and stop signs. For your regular commute, this may prove to be very easy.

Look way ahead in the distance; not just at the car immediately in front of you. If the car in front of you is very large and your visibility is limited in the distance, you may consider taking signs from reflections of brake lights on the wet road or on other reflective objects. In some cases, you can see brake lights through the car ahead of you.

Brake sooner! When you see a light turn red in the distance, slow down immediately and coast to the light, such that you never have to stop the car. By coasting to the light with some non-zero velocity, you are maintaining energy instead of wasting it all (by stopping completely). This is also much safer than braking at the last second, where gravel, oil, and other factors can cause accidents. As a note, you should not cross the intersection at high velocity as soon as the light turns green. This is dangerous, as aggressive drivers tend to speed up at the sign of a yellow light.

Engine Braking
Don't do it unless you need to slow down at a greater rate than possible by coasting. If you drive a manual transmission vehicle and do not have your foot on the gas and you do not need to slow down at a fast pace, simply depress the clutch and coast. In some areas with hills, this is possible for miles!

Keep the RPMs Low!
Don't accelerate quickly! Keep your RPMs low. Some vehicles have variable valve timing that engages at relatively low RPM (i.e. you don't need to floor the vehicle for it to engage). This can result in more available power at the expense of much greater fuel usage. Accelerating slowly also gives you additional time to anticipate upcoming slow areas, such as red lights or police activity.

Take the Slow Roads!
I enjoy my commute much more now that I've discovered some slow back-roads to travel instead of I-80. On a day without traffic, a commute through the back-roads is about 5 minutes longer than taking the highway. On a day with traffic, the back-roads can be 20 minutes shorter (or more). In addition, I can drive slower on the back-roads, thereby reducing the force of wind on the car. Wind resistance does not increase linearly with speed. In other words, if you double your speed, the wind resistance quadruples! Thus, there is a bigger hit in fuel efficiency between 65 and 70MPH than between 40 and 45MPH.


Conclusions
Drive slower, brake sooner, and avoid situations where braking is necessary! Also, do not accelerate quickly. Not only will your commute be more efficient, but you will likely find it to be less stressful and much safer. By utilizing the mentioned techniques, I was able to increase my fuel efficiency from 32MPG to 40MPG, and equivalent savings of about $7 per refueling at today's gas prices.