Energy tip #12: ease up on the acceleration, leadfoot

fastcar.gifLooking to save on gas money? You can save up to 37% simply by adjusting your style of your driving. If you have a tendency to accelerate quickly and brake aggressively, smoothing out the ride will give your tank some extra legs. Not to mention make your neighborhood a little safer.

You’d be amazed how much your of your car’s fuel economy is under your control. Edmunds.com ran some tests to determine the best way to save gas and driving moderately instead of aggressively came out as the #1 thing an individual could do to improve fuel economy.

As the author of these tips, I have to admit to a little reluctance to posting this one. I’m not quite a “Dukes of Hazzard” style driver, but I do occasionally like to lay the foot on the gas pedal. I’m interested to try this out myself, so anyone elso who wants to give it a go, please feel free to share your experiences.

Let’s look at how the numbers stack up:

Average miles per gallon: 19.6
Average miles/year: 12,000
Average $/gallon (US): $2.50
Average $/year in gas: 1,531
37% savings: $566
Lbs CO2 saved: 4,432



39 people last week pledged to check their windows and doors for costly leaks (Tip #11). At 2,800 pounds of CO2 saved per home improvement project, this would mean a savings of 109,200 lbs. Assuming 20% of people actually do the project, we can bank on about 22,000 lbs. of CO2 savings, or enough to take two cars off the road for an entire year.

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  1. Lynn - September 27, 2006

    Ooh, it’s so true! When I first got my Honda Civic Hybrid in 2003, I was obsessed with the instantaneous miles-per-gallon meter, and tried to squeeze every MPG I could out of slow acceleration and coasting. It totally changed the way I drive. My then-boyfriend made fun of me for driving like an old lady.
    Since then, we got married and he bought a Prius, and now he’s toned down his race car driving, too — his eyes are always on the 50+ MPG prize.
    (Hint: There’s also a sweet spot for drafting behind a semi, particularly on roads where the speed limit is 55 mph or less. My little MPG meter ticks up noticeably when I use this trick.)

  2. cindy - September 27, 2006

    I wish more people drove like “old ladies.” Not only for the sake of the environment and the sake of our wallets but it would make the roads a much more peaceful place to travel.

  3. robin - September 27, 2006

    i wonder–if you’re drafting behind a semi, does that increase the drag on the semi? that would make a difference in total (not individual) energy use.
    anyone know?

  4. AJ - September 27, 2006

    Definitely true. That’s the major reason why highway mileage is better than city. Less stop and go.
    About drafting semis – it works but it is dangerous. If the semi stops suddenly you’re in trouble as drafting requires you to be really close. Your car and/or your life is not worth the $0.37 you might save at the pump.

  5. Duncan - September 27, 2006

    Re: Drafting behind the semi and drag

    I’m pretty sure the answer is no, that it would not increase the drag on the semi. The drag is mainly due to having to overcome the air resistance in front of the semi; although the pattern of turbulence behind the semi makes a difference. Creating a smooth air flow around the semi would reduce aerodynamic resistance. But the effect of a civic behind a semi would probably be negligible on turbulence.

    A less than perfect analogy: when cyclists draft behind each other, it doesn’t slow the first cyclist down. In fact, I think there is a very tiny benefit for the lead cyclist. But all the cyclists are more or less the same size, so, as I said, a less than perfect analogy.

  6. Erica - September 27, 2006

    I don’t have a hybrid (YET!) but the car I do have has one of those MPG guages and I have to agree – It has changed my driving habits probably 95% of the time I am on the road. I use the cruise control at every opportunity as well and always watch the mileage I get tick higher every time! Love that thing!

    I think that maybe if the auto manufacturers had this guage in all vehicles we would see a fairly substantial change in peoples driving behaviors. Just another idea!

    Erica

  7. disdaniel - September 27, 2006

    *smacks head*
    You mean driving between 85 and 90 mph is not improving my efficiency? I’m driving for a shorter amount of time…doesn’t that count?

  8. Gregg - September 27, 2006

    Even being a considerable (read: safe) distance behind a semi can bring significant reduction in drag. When I am out biking, a semi can be a long ways out in front of me and I can still feel it breaking the wind for me. Obviously, a car travels faster than a bike and is wider, but I am sure you can still get a benefit from being behind a semi without being dangerously close.

  9. Anonymous - September 27, 2006

    If I tone down my driving any more I’ll get killed. By the aggressive drivers who are already tailgating me.

  10. Adam - September 28, 2006

    Top speeds matter a great deal. I’ve seen incredible mileage numbers in my ’03 Corolla by simply using the techniques handed down by little old ladies everywhere. EPA rated at 40mpg highway (5spd MT), my Corolla has been easily clearing 45mpg on the highway simply because I’ve kept speeds between 55 and 60. That’s getting into hybrid territory for a $10K used car.
    The math doesn’t lie. Wind resistance is a function of velocity squared. Assuming you are in your vehicle’s highest gear, increases in speed reduce your mileage exponentially.
    In addition, I challenge all of you to do the math on the time savings of speeding. Most of your highway trips are probably less than 30 miles. Run some numbers to see how much time 75mph will save you over 55mph. It’s probably about the same amount of time you spent snoozing or just staring at the wall comprehending last night’s episode of Family Guy.
    Come join me in the right lane. It’s actually quite relaxing.

  11. pradwastes - September 29, 2006

    A stick shift will give about 10% faster acceration than an automatic tranmission. The Stick shift will also give significantly better gas milage. On any car we have to make sure the tire pressue is at least up to spec. and drive like there is an egg between your shoe sole and the gas pedal with the exception of getting on the freeway. keep the speed down because the air resistance increases on a logerismic basis. Most cars will give the best milage at about 40 MPH. Going up hill takes more fuel than level. Think about riding a bicicle and you will get a goof sense of the speed. It can be useful to follow 6 feet behind a truck but this can get you killed. The EPA milage figuter do not tack in evrer using air conditioning or ever having to go up hill. The smaller the car and engine the less gasoline it will use. Ridng a motor cycle is fun and uses less gas. I can be dangerous

  12. Jason - January 5, 2007

    Drafting:
    another higher efficiency example would be NASCAR or other stock car racing. Two or 3 cars drafting will go faster around the track that just one car on its own. There must be a benefit for the first car… a little bit of a ‘push’ from the next car.

  13. Anonymous - April 28, 2007

    Drafting:
    In response to a civic trailing a semi: The semi would actually have less drag on it with a civic behind it. Although not a large impact, the civic would reduce some of the drag associated with the turbulent flow at the rear of the semi. Therefore, both the semi and the civic would increase in efficiency. This could be a good idea to reduce fuel consumption for drivers, since the semi would produce a considerable amount of low pressure behind it.

  14. Kyle - May 25, 2007

    I just drove my 2005 V8 mustang through two tanks of gas… both atound 70 MPH. The first tank averaged 19 MPG HWY. For the he second Tank i drafted 3 seconds behind a semi and got over 30 MPG!

  15. David - June 6, 2007

    The comment about manual vs. automatic transmissions is no longer true. The current generation of Honda Civic (non-hybrid) is rated for 40 MPG highway with automatic and 39 MPG with manual.

  16. Joe - June 10, 2007

    When driving my older Chrysler easier on the road I have noticed a 7 mile per gallon improvement over my aggressive driving average. I’ve also noticed that my driving speeds can affect it. I heard that most newer vehicles are designed to cruise well at normal road speeds, (30, 45, & 65mph). But at least with my car, those speeds provide the best mileage. It has to do with the gear ratios & engine resistance. Usually, driving about 3-6 miles faster than the speed where it shifts (during safe driving) gives me my top mileage. My favorite thing is to take advantage of down hill drives, because it’s partially free driving.

  17. Keith - November 15, 2007

    Dont forget to take surface wind speeds into miles per gallon calculations. Driving into a good head wind will lower your mpg. While its usually not practical, try to plan a trip with the wind behind your vehicle and you will save $$$$$$$

  18. Rob - November 24, 2007

    Kyle: That’s very doubtful. At 70 m.p.h. 3 seconds is over 300 feet. There’s no way that drag reduction could produce a 58% increase in m.p.g. at that distance.
    Feel free to read my comments on drafting, from both a safety and practicality point of view at:
    http://hamiltonianfunction.blogspot.com/2007/06/blog-post.html
    and http://hamiltonianfunction.blogspot.com/2007/06/practicalities-of-drafting.html

  19. A MAD TRUCKER - February 8, 2008

    IF YOU DRAFT US YOUR STUPID FOR ONE THING AND CRAZY IT IS ILLEGAL AND DANGEROUS I DRUG A LADY 2.5 MILES BECAUSE SHE WAS DRAFTING ME AND I DID NOT SEE HER I HAD TO HIT THE BRAKES AND SHE WENT UNDER MY TRAILER BY THE WAY IF WERE LOADED HEAVY WE WILL NOT FEEL IT

  20. John Law - March 20, 2008

    Drafting is not illegal. However rear ending a truck is illegal.

  21. Aero Engineer - March 20, 2008

    Drafting a truck. There is definitely a sweet spot. Go out of it and you will not feel the benefits but the buffet. Shapes with a blunt leading edge (the first part into the undisturbed air) and a sharp trailing edge (think wing section) are more efficient than a something with that is blunt on both ends, e.g. a truck. The truck lacks the geometrical reduction that allows the air to flow smoothly over the rear end of it. Vehicles drag the air along with them. It takes energy to create turbulence in the air. The more turbulence you see, the more energy that vehicle is loosing from its power plant to making the air move.
    The flow pattern of air moving over a blunt object is the same as the object moving through the air. When air or water move over a blunt object, there are large eddies generated at the trailing edge. This is due to the air not flowing smoothly over the object and separating from the last place t can tangentially flow. There is a pressure difference that causes the air to recirculate. The scale of this is relative to the dimensions of the object and the flow. For the truck, it is symmetrical with respect tot the flow so you can expect the large eddies to be on the order of half the truck width. They will detach and be drug behind for some distance but probably only on the order of up to 2 times the width. After that the large eddies break down into smaller ones rapidly and diffuse outward. In this region your car will be knocked laterally which will increase the force that your car needs to maintain its position. I.e. bad for your MPG.
    Issues of practical concern. You will be pelted with stones, you may be subject to a re-tread letting loose. Don’t know what that is? Ever wonder what all those long tire fragments of rubber along the road. Trucks cap existing tires with more tread. Often they fail and believe me, you do not want to be in close range of such an event. If you are close enough you will get definite boost in MPG. You should not however drive close to a truck in general. If you want to, carry a CB with you, when you are on a stretch of road that does not have significant traffic, then contact the truck and ask permission and let him know that you want to be back there. The main thing is to ask permission. Cause when someone cuts them off, they have to stop. If you are watching your old mpg meter and don’t see them slow down rapidly. You are screwed. If you are not really close, then the payoff is not that great to actually damaging.
    The aerodynamics benefit to the truck is small unless you develop a train of vehicles that are progressively smaller. But then you will probably cause a major accident if there is the slightest perturbation to the system.
    All of the discussion is choice. But choices must be made with regard for the whole community. It only takes one idiot to cut in front of a truck and your fun is over.

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