Tag Archive 'route'

Jul 11 2008

Choosing Your Route for Maximum Fuel Economy

Good fuel economy isn’t all about driving an efficient car or modifying your car. One of the biggest limiting factors is your commute. The length of your commute isn’t something you can do much about, but there is almost always more than one way to get somewhere, as long as you’re willing to spend the time and effort to do it. This article will examine what makes a good route and how you can use different environmental factors to your benefit.

Before I get into techniques to save gas with your automobiles, it’s important to mention that if your commute is short and your climate is hospitable you have the perfect opportunity to get in shape. Your bike (or perhaps your legs) will become your best friends; saving you money and keeping your body in good health at the same time, what could be better? Besides people power, public transportation is a wonderful way to go, and will only get better as more people choose to ride. The park and ride is an especially attractive way to go when you’re commuting into a congested and polluted city.

That said, even the most diligent public transportation users or peddlers will need to drive every once in a while, whether it be to work, school, or out on the town. The first consideration is how many places you need to go. If it’s more than one plan your trip so that you’re looping around rather then zigzagging back and forth. For such trips you will not perform them enough to do a detailed analysis so you should abide by a few simple rules for best results (on average):
- Take the shortest path through all stops
- Avoid areas with heavy traffic (especially those that noticeably affect your driving patterns)
- Try to avoid roads with lots of stop signs and lights
Of course these things must all be balanced, but for most trips there are obvious options such as cruising down the interstate versus going through town.

Now, for those trips that are repeated with great frequency a bit of investigation is in order. By investigation I mean using your instantaneous fuel economy display to log your segment mileage over the course of several days so that you can compare different routes to see if there is on that gives consistently better mileage. However, be warned that you may chose a longer route with better mileage but still be burning more fuel! This is one of the reasons instant feedback is so important. If your vehicle was manufactured in 1996 or later check out www.scangauge.com or look online for a used model for sale. If your car is older but fuel injected email me and I will see what I can do to help you out with instrumentation (I have had great success with a device called the superMID in my 1991 CRX).

I’ll assume that most people are not instrumented yet and describe a few common scenarios and how they affect fuel economy:

1. Highway – In most cases highway driving will give you the best fuel economy you’ll see. There are some truly amazing fuel economy drivers that do much better around town than on the highway, but for most of us (myself included) the highway is a good place to be. But don’t forget: slow down! I drive 55 on the highway; that 10 MPH may seem like a lot but it does not extend the trip time very much and boosts gas mileage tremendously. Because aerodynamic drag increases greatly with speed, short of serious modifications to the car, slowing down will give you the biggest gain on the highway.

2. Around Town – This is the killer for most people. Frequent starts and stops, especially when coupled with a heavy foot, destroy gas mileage. Avoid heavy traffic, speeds that do not allow you to use your highest gear, and areas that do not lend themselves to safe coasting practices. Even if it extends your trip slightly the highway is preferable to 25 MPH speed limits and frequent, unexpected stops. However, if you have to drive through town try to stay in the highest gear possible. Your best instantaneous fuel economy will be achieved at the slowest speed you can go in the highest gear possible. When in a 30 MPH zone I regularly achieve 80+ MPG instantaneous readings because my engine is only turning over at 1,000 RPM.

3. Hills – It may seem counterintuitive, but hills can be a fuel economy driver’s best friends. Sure, you’ll get bad mileage up the hill, but as much as you go up you will eventually go down, and on the downhill engine off coasting will seriously increase your trip’s fuel economy. Some of the best fuel economy drivers live in hilly areas that allow them to have their engines on for only 50-60% of their commute, which allows them to achieve phenomenal mileage on their stock vehicles. When considering a hilly route it is best to plan stops that will be at the tops of hills so that you can coast while going up a hill and use less gas to get up to speed as you go down the other side. This may be hard to do but even a few stops can make a huge difference. Also, hills allow you to practice a technique called “driving with load.” DWLing means slowing down up the hill and regaining speed on the other side. This gives the engine a break when it’s working its hardest both as it struggles up his and as it struggles to regain speed.

4. Lights – In many places lights are timed in order to allow drivers who maintain the speed limit to pass through with limited obstruction. If you live in an area with timed light do your best to figure out the timing pattern and adjust your speeds in order to minimize stops. If a light is red it still might change based on the timing, so if you know it well enough you can plan your coast to coincide with the change of the light and the anticipated pace of traffic. When you do get caught in a red light, don’t take off, start up slowly and shift low in the RPM range. Chances are you will get caught by another soon enough and you will have wished you wasted less gas getting up to speed. Also, by accelerating slowly you leave space in front of you where you can coast while coming up to another stop. If you are right on someone’s bumper you have to yield to their reactions to upcoming lights. Another thing is that when stopping you should use engine braking as much as possible. When engine braking you are burning no gasoline and also reducing wear on your brakes.

So generally, to wrap it up, instantaneous information is necessary for a detailed analysis, but in the meantime anyone can improve their commute by taking advantage of existing circumstances or finding another route that is more exploitable. If the interstate you drive down has a side road with lower speed limits, take that, not only will you have a more relaxing drive but the lower speeds will improve your fuel economy. If you launch from the light to get up to speed just to hit the brakes for the next light, start up a little slower, shift lower, and coast to the next light. It’s all about attitude, once you stop rushing through things you won’t feel as rushed to get them done.

A friend, who I consider a good fuel economy driver, took the time to write up a few details of his commute and technique for the site. Please check it out here. Thanks alot, Phil.

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