Updated on 04.17.09

Lessons in Fuel-Efficient Driving

Trent Hamm

One of the interesting features of our Prius is that it keeps a running tab on your current gas mileage. You can see both the mileage at any given moment or the average over your trip. Having such easy access to this information while you’re driving subtly teaches you how to drive more efficiently. Here are a few things we’ve learned.

Coasting makes a huge difference on your gas mileage. One thing this data has taught me is the huge value of coasting, particularly through a series of stoplights. Stopping and starting eats a lot of gas – our gas mileage during acceleration goes down to as low as 10 miles per gallon. Coasting, on the other hand, uses virtually no gas at all.

Before adjusting my driving, I had a strong tendency to leave a stoplight, accelerate to the speed limit in town, then often find myself hitting the brake and stopping again as I approached the next stoplight. That meant I was doing a ton of acceleration, then losing most of that speed by braking again just a block later.

Instead of doing that, I’ve found it’s just as quick (and way more energy efficient) to coast as much as possible through long strings of stoplights. I accelerate up to roughly the speed limit, then I coast for a while, particularly if the light ahead of me is red. Almost without fail, I catch up to the car ahead of me just as they’re accelerating away from the stop – and I already have some momentum going forward, which means I don’t have to accelerate nearly as hard to get back up to the speed limit. It doesn’t take any longer and it saves money.

I tested this out driving through the town where I live and the difference was tremendous – doing this added about 25 miles per gallon to my mileage through town.

Driving 75 on the interstate is substantially less fuel efficient than driving 55 on a two-lane highway. One regular trip for us is driving south to the West Des Moines area, about a 35 mile trip or so. We have two routes to get there that are roughly equal in length, but the interstate is a bit faster. On the interstate, of course, we drive around 75 miles per hour to keep up with the traffic. On the other hand, we can take the highway and go around 55 miles per hour. The highway usually takes us about six minutes longer to get to our destination, so before getting our Prius, we’d simply always use the highway.

But here’s the kicker. If we take the interstate, we would get around 38 miles per gallon. If we take the highway, we get about 52 miles per gallon. So, if we take the interstate, we use 0.92 gallons, but on the highway, we use 0.67 gallons. That’s a savings of about $0.48 on the trip, even in our relatively fuel efficient car.

This changes the equation just a little bit. The two lane highway is far more scenic than the interstate as well – there are many more interesting things to see and talk about along the highway route (meaning it’s easier to engage the kids). When you also toss in the fact that it’s cheaper – and it would be a much bigger difference in a less fuel-efficient car or if the price of a gallon of gas were higher than $1.94 – the balance starts to shift towards the slower route. Does the balance actually shift? Not entirely – for us, it still depends on a number of factors (the time of day, the presence of kids, and so on) – but the balance of values has changed.

Wind resistance makes a tremendous difference in your drive. Simply put, driving on a windy day (unless the wind is consistent and at your back) is incredibly inefficient.

On a recent windy day, my family and I embarked on a lengthy road trip where the wind was mostly in our face. This forced us to accelerate quite a bit more to maintain speed – and it pushed the gas mileage down about 35% (29 versus 44). As a test, I drove with the wind on another windy day and found that it improved our mileage by only about 10% (48.5 versus 44).

Thus, unless the wind is very, very consistent and at your back, a windy day will hurt your gas mileage. If you have an optional trip to make and there’s a heavy wind outside, you’re better off delaying the trip. That’s what I’ve already done twice since seeing the impact that a heavy wind can have on gas mileage.

Turn off your cruise control in hilly areas. In virtually every car I’ve used, cruise control has been a great tool on flat roads. It helps me control my slight lead-foot tendencies and seems to do a good job with gas mileage. The data from our Prius backs this up – on flat roads, that is.

If you enter a hilly area, though, cruise control is very inefficient. Instead of maximizing your speed going down hills and using that momentum, cruise control instead tries to keep the car within a few miles per hour of your set speed.

Since it can’t read the road ahead, it doesn’t know what’s coming up. You do. Take advantage of that and turn off the cruise control in hilly areas. I turn it off any time I go downhill or uphill, since it seems to be more efficient to build up speed going down the hill (getting well above your cruise speed) then coasting at the bottom until you get back to your cruise speed, and doing the opposite on hills (allowing yourself to get well below your cruise speed instead of accelerating into a hill).

In the end, our best value from the Prius might be the ability to actually see how our little driving choices affect our gas mileage – and how we can make better choices to vastly improve that mileage. As time goes on, these better choices become ingrained in our driving habits, making the more efficient choices our natural choices – ones that we’ll carry on to other cars. Fuel efficient driving doesn’t cost you time – it just saves you money.

Personally, I’d like to see all cars have a fuel mileage indicator. It’s been an invaluable tool for directly teaching someone how to drive more efficiently – and it’s easy to see the benefit when you go to the gas pump.

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  1. Cyllya says:

    I’d also like such a display. I heard there’s a thing you can buy and put on your dashboard that beeps when you’re doing something gas-inefficient. Not as good as the display you’re talking about, but probably better than nothing.

  2. J says:

    For those looking for a way to get a MPG readout, you can pick up a scangauge that will read right from the diagnostic port of your car.


    In addition to providing MPG information, you can get water temp, throttle position and read any check engine codes that might come up (as well as clear them)

  3. Chad says:

    Changing your speed so much on hills is a major disruption to traffic flow, please don’t do that unless you’re the only one on the road…

  4. SJ says:

    Actually you know what else would be cool? If it had internet and could see the avg. price of fuel and pop up w/ a $/mile or a $/minute =)
    Or how about CO2 per second!

    I mean, treadmills have all these settings, doesn’t sound that much more difficult =D

    (Or even if you just input the avg price manually…)

  5. Jonathan says:

    You can add a “ScanGauge II” to any car 1996 or newer. It will give you up to date gas mileage along with other metrics.

  6. Baker @ ManVsDebt says:

    Interesting data for sure. I’m not positive any of this would be enough to significantly change my driving habits. It’s hard to say!

  7. CPA Kevin says:

    That is a great feature, it would be nice to see that kind of instant feedback instead of just calculating it whenever you fill up.

  8. Kevin says:

    I believe all Nissans (and Infinitis) let you see your instant as well as your average mileage.

  9. Kiran says:

    I work in the energy industry, and I’ve thought that the best thing would be to require all new cars to have an instantaneous MPG display. Probably improve fleet efficiency by 5+%, and probably far cheaper for auto manufacturers.

  10. David says:

    On a roadtrip once down the Columbia Gorge (in Oregon), our Chevy Astro was averaging fifty one miles per gallon due to a HUGE tailwind (seriously, it was probably going faster than us). Normally, those vans are quite the fuel hog.

  11. Glad to finally see this blog take on a topic so close to my own heart, :)

    PS: Do you have a goal in mind?

  12. Abby says:

    My Ford also allows me to see instant and average (over lifetime or trip) mileage.

  13. Natalie says:

    My Volvo does the same thing… its not just a special Prius thing.

  14. Johnny says:

    The relationship between fuel usage and speed varies by automobile. Gear ratios and transmissions play a big role. My cars peak gas mileage is at about 55. However, I’ve had a van that would be most efficient over 80 mph.

  15. John says:

    I drive a big truck and pay for my own fuel, as you can imagine, fuel economy is a huge concern for me. I track my MPG as well as cost per mile and several other things. If you dig around a little online you can find a white paper that Cummins did about fuel milage. It is a very interesting read and many of the things can be applied to regular passenger cars.

  16. Michelle says:

    My 2005 Ford Freestyle has an MPG display, and I think it’s fun to see what I can do to increase the MPG. It’s almost like a game to me.

  17. Morder says:

    heh, my 1990 BMW does that – they’ve probably had that feature in their cars for years. Great feature – won’t buy a new car without it.

  18. Jeff says:

    This sort of depends on where you live. If you live where I live (downtown Chicago) and you coast all the way to the stoplight, then me and a dozen other cars and cabbies will be all over your bumper. At least do this in the right lane.

    And the highway thing sounds good, but I can’t imagine I’m the only one that finds the people who vary speeds by 15 mph from uphill to downhill to be extremely annoying.

  19. TJ says:

    I recently test drove a Yukon XL Denali, not a fuel efficient vehicle but we have twins on the way and will need a much larger car. It had the instant fuel efficiency, along with trip efficiency. It was quite handy.

    Also you can drive 55 or 60 in the 70 mph zone, and save a bundle. In my Pontiac I figured that just by slowing down on my daily interstate commute, I went from 22 mpg to 25 mpg.

  20. Jeff says:

    My first car was a hand-me-down 1984 Cadillac that had a fuel mileage indicator. It definitely affected the way I drove, because it was always a challenge to stretch my fuel as far as possible. Of course it helped that I was 16 years old, had no money, and the rusted out gas tank only held half of its intended capacity. These were all great motivators to conserve fuel.

    Since the old Cadillac, I haven’t owned another car with that feature…and it’s the one thing I routinely miss. It should be standard equipment!

  21. Colin says:

    $0.50 for six minutes is $5/hr. My time is worth more than that if strictly comparing gas price.

    Really, though, if you want to improve mileage systemically then get rid of the number of stop lights. Get rid of as many reasons to take all the built-up kinetic energy of accelerating that is literally burned away when you brake. Reduce idle time.

    More roundabouts.

    More Michigan lefts.

    More superstreets.

    More U-turns to avoid left turns across traffic.

  22. jc says:

    MPG gauges are often “features” in upscale or cruising option packages. but i’ve seen very few in fuel efficient small cars (apart from small hybrids like the prius) like a civic or corolla

  23. lurker carl says:

    Most factory installed fuel monitors can not be calibrated and tend to err by as much as 25%.

    Any automobile from model year 1995 or newer with the OBD2 can use a device called ScanGauge. Among the host of engine functions it monitors, it’s ability to allow the driver to maximize fuel consumption is the function that pays for the device.

  24. kristine says:

    By coasting, do you mean just not stepping on the gas, or actually switching into neutral?

  25. The new Honda Hybrid is supposed to have a green display light around the speedometer that comes on when you drives in a manner that is fuel efficient. I believe it turns blue when you drive in a non fuel efficient way. Maybe a little easier than trying to constantly read and compare numbers.

  26. Oh, I would LOVE to have an MPG calculator. I try to hypermile, but it would be really cool to actually see my efforts working.

  27. It sounds like you are having a lot of fun with the new car. I’d love to have that feature in my car, but would probably spend too much time looking at my MPG that I’d end up in the trunk of the car in front of me!!!

  28. Nick says:

    I don’t want to be a whistle blower here, but the difference in that trip is 10 minutes, not 6. I mention this only because you occasionally take the time to calculate very specific things, but sometimes are sloppy with your estimates…

    That’s a pretty paltry hourly rate given that you said you wouldn’t bother taking 20 minutes to save 10 bucks a week or so ago.

    Seems like the money saved isn’t worth it unless as you mention there are other variables like a scenic drive or maybe just being more environmentally friendly.

  29. Joey says:

    @ Nick:

    Don’t worry, the contradiction of buying a new $22,000+ car he couldn’t afford with cash after years of crowing about the need for smart financial decisions far outweighs the contradiction of his trumpeting saving $.48 per trip after declaring his time worth more than $30 per hour.

  30. shadox says:

    In recent months I have improved my car’s gas mileage by about 15% simply by watching my acceleration and speed. My old 1997 Geo Prizm now gets about 31 miles to the gallon when I drive sensibly. Money saved and emissions reduced.

  31. George says:

    Contradictions can be fascinating when reading Trent’s blog :-)

    Hyundai Sonata has the fuel monitor. Trent’s observations match my own with the Hyundai (on my daily commute, I get 24 mpg if I drive like I don’t care and 27+ mpg if I do it right), but he left out the effect of tire pressure. Probably hasn’t had the car long enough for the tire pressure to drop (and fuel consumption increase)?

  32. andrew says:

    I personally think driving does MUCH more towards helping MPG than any hybrid car. Getting 44 MPG with a hybrid is not very good considering a Geo Metro (which holds the same number of people and supplies) gets almost exactly the same. And since you can get a used Metro for a couple hundred dollars, or a few thousand for a nicer one, getting a hybrid is really a rip-off.

    Driving 15 MPH under the speed limit on an interstate is illegal and dangerous. It’s called impeding traffic. It’s not a good idea.

    Shifting into neutral (in a manual transmission car) to coast actually gives you worse MPG than coasting in gear. The way that modern engines work, you use essentially no gasoline while engine braking–coasting in gear. I don’t know which is better in an automatic, but if you really care about mpg you should be driving a manual anyway.

  33. KC says:

    My mother has an 07 Avalon with the MPG display. Dad and I have toyed around with it and there doesn’t seem to be significant change even when in the obvious stop and go of a large city vs. driving a steady speed on an interstate. It always seems to hover around the same setting (about 25 mpg). We even drove like a bat out of hell through the city – accelerating very quickly up to the speed limit, but didn’t see remarkable change – so I’m not sure I trust those gages.

    I have an Acura TL and I get between 31-33 mpg whether I go 65mph or 90mph on the interstate. I’ve tested it several times on quite a few trips (basically you can go 90 all the way to St Louis, but you can’t get above 65 most of the way to Nashville – both are over 3 hours away). I get very similar mileage as long as I drive consistently (yes you can be inconsistent on the interstate using more fuel than necessary.) As for driving this car in the city I do see quite a bit of change in mpg when I use fuel saving techniques like coasting. The worst city mileage I get is 17mpg, best is around 23.

    But 55? No amount of money can make me drive that slow when the posted speed is 65 or higher and there is low traffic. In fact I have a hard time going 55 even when that is the posted speed.

  34. KC says:

    Re-reading the posts I noticed someone commenting on the varying speed going uphill and down hill while driving. I got behind a Prius one time making the 45 min trip to my inlaws on a rural highway. The Prius was varying its speed quite a bit and it was really, really annoying. I was patient and didn’t tailgate, but it was hard cause I naturally drive at a consistent speed. Finally this guy pulled over and let the traffic pass. I kept thinking – doesn’t he have something better to do than drive slow and achieve maximum fuel efficiency? Doesn’t he have someone he loves and loves him to spend time with rather than saving a few pennies by driving efficiently? I really don’t understand this line of thought – maintain a consistent speed and get to where you are going as safely and timely as possible.

  35. Mark says:

    The interstate vs. highway argument is spot on. I made a recent trip from Chicago to eastern Iowa, and took the highways instead of the interstate that charges tolls. I took advantage of coasting and light gas applications as much as possible. My car, a 2005 Hyundai Sonata 5-speed manual, is rated for 30 MPG on the highway, but I squeezed out 39! Not kidding! I had to run the numbers multiple times to make sure I got them right. No need to get a hybrid!

    Granted, it’s a stick shift, which usually helps with mileages. But this just goes to show how much we could achieve by simply re-educating our driving population.

  36. Interesting that you can monitor precise moments– wish I could do that. We could all benefit from that insight . . .

  37. I always wondered what kind of effect these efficiency tips would have on taxi cabs. They spend so much money on gas and so much of their time on the road, that there has to be something to it.

    On the other hand, if I hop in a cab and the driver is coasting or not starting and stopping as quickly as possible to get me to where I’m going fast, then he/she probably won’t get tipped very well.

    I wonder what the perfect balance between the two is….

  38. Leah says:

    I just keep track of my mileage every time I fill up at the pump, and that allows me to roughly know my fuel efficiency (granted, over a tank’s worth, but still). I’ve been doing all of the above tips for years, and I definitely see the help in my mpg. I also notice the dip in mpg when my boyfriend drives my car instead, and I’ve been teaching him my techniques so that we can both save.

  39. Evita says:

    I am reading this post on Earth Day….. how appropriate! and food for tought….

    Unfortunately, I am stuck with a 7-year old thirsty Cavalier and a chauffeur (hubby) who loves “sporty driving”…. “green” driving will have to wait!

  40. DB Cooper says:

    I don’t need any kind of calculator to tell me that stopping and starting, quick accelerations, driving up hills, or driving into the wind burns additional energy – or that coasting saves fuel…all I need to do is go out and ride my bike. Riding a bike teaches all these concepts – you get immediate feedback in your legs and your lungs. It’s certainly not rocket science!

  41. Valerie says:

    That’s the way my Dad has always driven – watching out for the lights ahead and moderating his speed so he doesn’t stop or accelerate often. He doesn’t waste a lot of money! ;)

  42. Golfing Girl says:

    You might want to factor safety in your equation. I could be wrong, but I believe the interstate is much safer than a two-lane highway where cars can easily cross the yellow line…

  43. Randy says:

    Good information. I had a Chrysler van with instant mpg and it actually caused problems. I played games seeing how high I could make it go (seemed to have a limit of 99) and how low (0). Once I realized that I was watching the guage instead of the road, I stopped playing.

    As noted earlier, 48cents saved over 6 minutes us $4.80/hour (with acknowldgements to different figures above). Not much of a savings, unless you count the scenery, kids, etc. Sometimes I take the longer trip just to avoid the scenery, kids, etc.

    Regarding building up speed going down a hill, you have to be cognizant of the speed limit and minimums. One ticket can wipe out a LOT of fuel savings. “But officer, I was trying to save gas” probably won’t get you out of a ticket.

    Good information overall and a good reminder.

  44. Kenny says:



    I have had two vehicles with these “instant gas mileage” trackers, and when I use real math to divide the miles I go by the number of gallons I pump into the tank, the hard numbers are usually below the trip computer’s.

    For my green minivan, the trip computer sometimes says an average of 21 miles per gallon, but real math worked out to less than 19 miles per gallon. It was disappointing to discover that my fuel economy for the minivan sometimes is 10% worse than what the computer tells me.

    I am interested to learn if your Prius may have the same affliction.

    Other than that, I am happy you point out these seemingly obvious tips. As you know, common sense really isn’t that common!

  45. Kenny says:


    A good book to read is TRAFFIC: Why we drive the way we do (and what it says about us) by Tom Vanderbilt.

    There’s a part that addresses your interstate vs. highway decision, as well as convincing arguments for roundabouts and other things that seem dangerous and slow at first, but as a result tend to make things safer and quicker for everyone.

    I know you like to review books and all…

  46. theCase says:

    As Lurker Carl said, you can buy a ScanGauge to do all this.

    One can also enter the price of gas and monitor cost per mile/ hour/trip/day etc. In addition to all the mileage tracking stuff it also allows one to READ and RESET ENGINE CODES, track engine temps, horsepower, throttle sensors. It plugs into the OBD port under the dash and cost $160 (I think). It’s a sweet little device and well worth the cost just for the ability to read and reset your engine codes (in my opinion).

  47. Jon says:

    Congrats on the Prius purchase! I was in a very similar situation to buy new, used, or keep my 9 year old car. I went with a new Toyot Rav4, which is certainly a no-no for multiple reasons. But honestly, why should you have to justify your purchase? We have a bunch of self-righteous commentors who use anonymity as a guise to say whatever they feel.

    You were in the position that you ‘could’ have paid straight cash for the Prius. Water under the bridge, but I didn’t post on the original article, so that’s my feedback.

    Now, to your point with the instant MPG’s — it’s amazing. My Rav has the same feature, and my wife and I use it constantly. I always assumed there was a ‘sweet spot’ for the speed you drive, but I never knew what it was until now. On my Rav, I went from 24 mpg interstate to 32 mpg interstate from dropping my speed from 72mph to 65 mph. That’s a massive disparity. Needless to say, no more speeding for us!

  48. SteveJ says:


    I have the people on my bumper issue, as I’m a natural coaster. My first few cars were little four banger sticks with 1.XL engines, so I started out with no oomph and a strong desire to avoid changing gears.

    The right lane is no good though, everyone is turning, thus you stomp on your brakes and negate that momentum.

    I find when I drive on the 4-6 lane roads around my house the same pattern repeats itself. I’m going faster than anyone else. An aggressive driver gets behind me to get ahead. I notice the light turn red, I take my foot off the gas. The driver behind gets a little road rage or whips around me. They get stopped at the light, my momentum carries me through it at 30 mph, I’m traveling faster than everyone else, repeat for 3 miles.

    Naturally I don’t particularly want to be near the driver who is burning his/her brakes, but I have a hard time changing my habits, and the desire to avoid braking does not equal the desire to go 5 under the speed limit.

  49. PF says:

    I have a 2002 Acura MDX that has the MPG readouts for both current and for the trip. It’s fun to watch. My overall gas mileage goes down by a couple mpg in the winter time due to winter driving and AWD. In the morning, I drop down 4000 vertical feet to go to work and my gas mileage is awesome, but boy does it tank on the way back up those 4000 ft in the afternoon.

    I don’t think there is a contradiction regarding Trent’s time. He said he would not spend 20 minutes in line because it would take him away from his family. In this scenario, his family is in the car and he is spending more time with them.

  50. ScottC says:

    I dislike people who slow down going up hills mostly because cars vary in their torque and ability to accelerate, in addition to the fact they have different mass. What may be efficient in your car might make me step on my breaks when I would otherwise be coasting. You accelerate quickly after climbing the hill, but I have to shift gears in my manual, wearing down my clutch just a little more.

    Further, it is inconsiderate and inefficient for others to vary your speed greatly. People have all kinds of reasons to be traveling at the speed limit on any given road. In many hilly areas there is no place to pass, which means everyone behind you must conform to the peculiarities of your car combined with your attempt to save 50 cents.

    Further, as you are probably well aware, traffic jams and slowdowns often have no cause than one driver traveling slowly. Here is a demonstration:


    (use the uphill grade simulation, start with trucks on, then remove them entirely. You’ll see that the traffic jam never goes away as long as traffic inflow remains high.)

    People naturally change space between cars based on speed. When you slow down, cars behind you get closer together. When you accelerate, each car waits until there is some space between it and the car in front of it before it starts to accelerate. As long as cars keep reaching the back of this compression wave before it dissipates, it will last perpetually.

    In short, you are actually hurting net efficiency by driving erratically and causing other drivers to slow down. On a busy road you could potentially create a traffic jam or slowdown that lasts for hours, even though you never vary your speed more than 10 miles above or below the speed limit.

  51. Jason says:

    For a while now, I’ve had an idea about car companies integrating topographical maps into their onboard gps systems to allow the vehicle to adjust the cruise control based on its up coming incline/delcine.

    What do you all think?

  52. Ted says:

    You basically just described the basics of something called “hypermiling”, something I discovered last year when I was still in college. I drive a 1996 Toyota Camry and I was averaging 20-24 mpg around town driving how you described you used to drive. As soon as I started paying attention to my foot a little more and applied the basic principles of “momentum conservation” in town, I went up to a staggering 32mpg which is almost 50% over the EPA estimated millage of 21mpg. On the highway I slowed down from 75 to 60mph (65 when speed limit increases to 70, staying in right lane) and stopped using cruise control, except on exceptionally flat roads and increased my millage from 30ish mpg to upwards of 40mpg.

    Great way to save the life of your car and save some cash along the way.

  53. Ruth says:

    I think having family in the car would be the most significant factor. Coming home from work TO my family, there is no way I would drive slower to save $5 per hour. With my family in the car with me, what’s the hurry?

  54. Borealis says:

    These tactics are great in moderation. But it is not worth it to cause road rage or dangerous traffic situations from those who aren’t practicing it. One accident will wipe out a lifetime of frugal driving.

    Moreover, there is a tendency to not drive in the right lane where cars are often slowing to turn right, but doing this in the left lane can be dangerous.

  55. Jared says:

    My 2004 Toyota Camry does the same thing. However, like comment #33, I always find that when I do the math myself, that it is less. Keep that in mind.

  56. Jim says:

    ScanGuage II is an awesome product. It give the instant MPG, Trip MPG and Tank MPG and Previous day MPG. I drive a 2007 Toyota FJ Cruiser and went from 16 to 19.5 MPG by using it.

  57. Andy says:

    Jason @38 — the topo maps would have to be very precise, which most maps aren’t. How about a front mounted radar unit?

    “This forced us to accelerate quite a bit more to maintain speed . d. .” technically acceleration is a change in speed, so no acceleration occurs at a uniform speed (except when turning, but thats a different story).

  58. Bill in Houston says:

    I have a lead foot and I know it. That’s why I’m happy to average 25mpg during my weekly commute. If I’m not sitting in traffic on one freeway doing 15 mph, I’m on another tollway doing 80. Averaging 80 I also manage 28mpg from a 2006 Altima when I take trips. I keep my car tuned, observe all maintenance schedule appointments, keep my tires inflated and balanced, and use the cruise control. Southeast Texas is flat as a pancake. The only hills are on the freeways.

    It is more about maximizing my time for these trips. For anything more than a seven hour drive, I fly.

    Trent, if you’re reading: What kind of mileage does that Prius get at 80? I could never own one of those. I’ve sat in them as a passenger and my shoulders are much too broad for the seats (in an ’07 model, anyway).

    Note to hypermilers: Please stay out of the left lane. It is for passing. Thank you.

  59. Bill in Houston says:


    Trent mentioned a windy day messing with your fuel economy. That is true to some extent, but it depends on your engine’s power output. If, for example you have a car with a total engine output of 100HP, driving into the wind will have a significant effect on your engine. It takes an average of 75 HP to maintain 100mph. Bear with me here; I know you’re not driving 100. I’m illustrating wind resistance versus horsepower. The Prius hybrid system puts out a maximum of 110HP. Your top speed would be about 113mph, so driving into a 43 knot wind you’d max out at 70. You’re using a much higher percentage of the system’s power output to overcome wind resistance than the 200HP on my car, meaning my mileage decrease percentage would be less.

    Okay, I can exhale now.

  60. Tom says:

    Excellent advice. My commute is about 40 minutes each way down a two lane county road with many stop lights and a 45mph speed limit max. Its amazing how many drivers don’t understand that it doesn’t matter how quickly you can get to a stop light (you’ll still be delayed the same amount of time).

    This website really helped me out in my conversion to being a more efficient road traveller:

  61. tammy says:

    I drive a 1998 Jeep Cherokee. I batch errands and only drive once or twice a week. When the gas crisis hit last year, I read about hypermiling and was intrigued. I am rarely in a mad rush to get to anywhere (thank goodness those days are over) and I’ve realized I can pretty much coast on roads around my house that have 25 mph speed limits. There really is no rush to fly off the line at a green light and rush to the next one.
    I’ve long given up the dragstrip….
    Great post – I so enjoy this blog and all the comments are incredibly enlightening.

  62. Jason says:

    @Andy #42

    You’re right about having to be precise… but it sure would be cool.

  63. Jade says:

    Gosh, I wish I could drive like this more often. Unfortunately I live in the big city where people honk at you for stopping at a stop sign, let alone doing the speed limit, or not racing up to a red light only to slam on your brakes.

    Even when I drive out to the suburbs to look at houses with my grandma, we usually follow our realtor around, and the way he drives I’m very grateful that gas is cheap right now, and I hope we get a house and close escrow before gas prices go back up…

  64. shortly after college before i was fully on my own feet i drove my dad’s 2003 honda insight which has one of those indicators and it is really amazing to see how much these things can make a difference

  65. Jim says:

    I also discovered hypermiling after we got a vehicle with a digital mpg readout. It isn’t even close to as fuel efficient as a Prius, but I can still get a lot better mileage if I pay attention to what I’m doing.

    I found pretty much the same results as Trent, with a couple of additions.

    1) Hypermilers say that any time you step on the brake, you’re wasting gas. They love to coast, like Trent. But only until they reduce speed enough to make the corner. The faster you can take the corner, the less gas you waste slowing down and speeding back up. There are limits to how fast you want to take corners, but that’s a personal preference thing. Most of us would rather maybe skimp a little on the efficiency and be safer around the corners.

    2) For gasoline engines and automatic transmissions, the sweet spot for speed v.s. efficiency seems to be at the lower end of the upper gear. Watch your tachometer, and when the needle dips, indicating it just shifted, that’s the best efficiency for that gear. Just after it shifts into high, that’ll be close to your best speed. Not sure if it’s the same for Prius, what with the electric motors and all.

    3) Running the air conditioner will reduce your efficiency a lot. When hypermilers are competing, they have stories of using ice-cooled radiation suits to keep cool without using the AC. Rolling down the windows will also reduce mileage somewhat. You could being a squirt bottle.

  66. Sharon says:

    The idea of using the momentum of downhill to get up the next hill is a big problem. You will end up, if there is any traffic at all, speeding when you go downhill, tailgating the law-abiding person going down the hill and endangering his/her life. I have had many a semi-truck do just that. I’m sorry if you don’t like the speed limit. That doesn’t mean that in your quest to get maximum mileage you get to kill me.

    Please don’t do this! It doesn’t do you and your family any good, either. And if you total your expensive new car, the extra you paid for the fuel efficiency goes straight down the drain.

  67. Sharon says:

    I like the pretty drives, too, but those lovely two-lane rural roads have a much higher death rate than the interstates. Something about “head-on” collisions…

  68. morrison says:

    My ’08 Ford Focus comes with an mpg gauge, plus it lets me know how many more miles I can go before I run out of gas. It also let’s me know when the tires need air.

    So far, on the highway I get 44-46 miles per gallon. Locally, around my rural homestead, I get 36 to 38 miles per gallon. The car is designed to hypermile/coast/whatever you want to call it, naturally, when I lift my foot off the gas pedal. It has cruise control, which I do use on the highway.

    I noticed a lot of commenters here, who have Fords, noted that they get good gas mileage.


  69. My basic premise is “if you see a red light, stop accelerating”. I find other eco-safe driving tips to be a bit fiddly for my tastes. Coasting is wonderful. Anything else is too much to remember for my poor brain!

  70. Huck says:

    Maybe someone mentioned it and I didn’t see it but here is a less expensive ($40) DIYish fuel usage monitor…the MPGuino

  71. Dave says:

    I drive a ’02 Hyndia Accent stick now, I get ~37mpg around town 40 on the hiway, most of the tips that people talk about lower my mpg, I found if i rev it up good ~ 3500rpm I get better then lugging it. Horsepower is horsepower high torque low rpm or low torque high rpm, engine and transmission efficence changes with load and speed. you have to find the best match for your own car.
    As for speed, again every car is different, it would be nice if the car companys would list drag coaffence, for the lower the C of D, the less speed changes mpg,
    I’m still up in the air about leaving it high gear or in neutral/cluth in coasting down hills.
    As for slowing down going up hills and speeding up going down, I tipicly only slow down ~5mph up, then it depends on how steep the down is.

  72. I’ve posted several blog articles discussing this very subject. I’ve learned a great deal about fuel efficiency, and that your car is only as fuel efficient as you are as a driver.

    I see a lot of that “hurry up and wait” driving people do, and it aggravates me. Why are you going to accelerate between speed humps? Why are you pressing the gas when you can clearly see the light ahead of you is red?

    Everyone’s in a hurry, and they’re losing money and harming the environment in the process.

  73. Jen says:

    Did you really mean a 25 mpg increase from coasting in town? That has to be a typo.

  74. PF says:

    People bring up a good point about the 2-lane roads and safety. Trent, do you still have your daughter rear facing? the American Academy of Pediatrics recommends rear-facing until the age of two. If you drive these roads a lot, you may want to consider turning her back around if she isn’t currently rear facing. Here’s a great video on rear facing.


  75. Dallas says:

    A few others have mentioned hypermiling in the comments, here is an article about people who take it seriously. It’s a great read.


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