Does Cruise Control Make Cars More Fuel Efficient?

Here lately I have become a real road warrior.  It is rare for me to hit the road this frequently, but with my mom’s hospitalization I find myself traveling back and forth a few times a week to visit.  Thank goodness gas prices came down when they did! While burning up the interstate back and forth I found myself switching to cruise control during open stretches, and wondered if I was saving gas in the process.

Does Cruise Control Save Gas?

Because I am not the most mechanically inclined person alive, I turned to a popular, well-regarded source for automobile information.  The Internet.  Seriously, what can’t you learn about on the Web these days!  A quick search of Google yielded a few promising results, but one in particular stuck out.  Edmunds.com, the popular website for automotive consumers, had this to say in an article on tips for improving fuel efficiency:

“Using cruise control can improve your gas mileage by helping you maintain a steady speed, but only if you are driving on mostly flat roads. If you are driving in hilly terrain, using cruise control typically causes your vehicle to speed up faster (to maintain the preset speed) than it would if you were operating the accelerator yourself. Before you push that cruise control button, think about the terrain ahead.”

Makes sense to me.  In fact, one of the things I noticed when pulling the few hills I encountered along the way was the car held back a little on the downhill and lost momentum,  requiring more gas to pull up the hill that followed.  Had I disabled the cruise control I could have simply allowed the car to gain some speed and then coasted up the first half of the next hill.  Careful, a speeding ticket here will wipe out any potential savings!

Putting the Theory to the Test

Using a highly unscientific test, I filled up the gas tank and traveled my normal route maintaining about the same speed (65mph) all the way, but leaving the cruise control off.  When I arrived home I made a mental note of how much gas I had consumed–about 1/3 of a tank.  A week later I filled up again before setting off on another trip and set the cruise control to the same speed I had maintained manually.  When I returned home I had used just over 1/4 of a tank.

What does this prove? Well, without running more tests, I doubt very much, but it is interesting that I appeared to use up less gas when running with the cruise control on.  Of course there are several variables to consider such as traffic, weather (was I running the AC, or driving with windows down), wind conditions (a strong headwind could cause additional drag), speed (65mph was probably a little high for optimal fuel efficiency), tire condition, etc.  In the future I will probably take Edmund’s advice and use the cruise control feature during long, flat stretches of road.

I’d love to hear from someone who knows more about cars than I do.  Does using cruise control really reduce gas consumption?

Comments

  1. I use a similar technique to obsolete29. Most of my route to work is flat, but the last stretch has a sizable hill. I usually cruise at 70 km/h on the flats and let it fall off to as low as 50 km/h going uphill (don’t want to make other drivers too angry…). Then when I get to the top, I’ve found that if I set my speed at 80km/h for a short stretch, I can coast the entire remaining distance to my parking spot.
    I’ve found that the trick to better mileage on my car (2003 Chevrolet Malibu) is to keep the RPMs between 1000 and 2000 – Lower is better. The higher the RPMs, the more fuel your car needs to burn to get them up there.
    The other important ingredient in better fuel economy is keeping your tires properly inflated or even a tiny bit over inflated (no more than 5psi over). Check it weekly.
    I’ve found that using these techniques has stretched my fill ups from once every 4 work days to once every 6 or 7 work days (depending on what errands I run on the way home). My round trip commute is a little over 66km.

  2. Most of the newer vehicles on the road today do have sophisticated engine management programs helping the driver (including cruise control, electronic stability control is another example).

    Edmunds is pretty much correct in stating that in most conditions crusie control can help with fuel efficiency (hills will kill your MPGs gained via using cruise control).

    Some higher end vehicles actually offer a radar based cruise control system, which is pretty cool.

    http://www.scordo.com/blog/blog

  3. Well, I’m not sure about cruise-control but I know by selling my car last week and choosing to cycle everywhere, that I am much more efficient both in terms of cost and gas used!

    But seriously, there are so many other costs of keeping your car over and above gas, it’s almost sad now I think about how much I used to waste just owning a car, let alone driving it.

  4. There’s nothing magical about cruise control, you use the same amount of gas to maintain the same speed with your foot on the pedal. I did a 2 year long experiment and tracked my mileage religiously. The biggest impact on mileage comes from stop and go driving. I got a job close to home (2.5 miles) and saw my mileage in my 2005 Tacoma drop from 25 to 16.5 MPG.

    To get a more accurate result you’d have to fill up before a trip and fill up again right after to figure out how many gallons were consumed. You’d then have to repeat the same trip with cruise control on so you are comparing apples to apples.

  5. @Andrew: Thanks. As I indicated, my “eye-balling” the fuel gauge was less than scientific–much less! Sounds like you have done more extensive testing. I’m leaning towards the belief that cruise control should only be used on level stretches of highway with no traffic. Even then, I’m not sure it is much of a gas-saver.

  6. @Andrew. Cruise control may actually manage engine performance (fuel push through, torque, etc.) a little more efficiently than breaking and accelerating manually. It’s the same principle behind ESC (stability control) which applies braking and engine management when the computer notices wheel spin or excessive breaking; a “normal” driver cannot perform the same task with the same safety and efficiency.

  7. I have to commute to work about 3 times a week (87 miles one way) and I use my cruise on the mostly flat stages and manually navigate the hills… disengaging the cruise and traveling slower up the hills and coasting down the other side. Once I’m back to normal terrain, re-engage the cruise; best of both worlds.

  8. The approach used by obsolete29 is valid, although a bit different than mine.

    The main point is that you have to gently accelerate a bit to gain sufficient speed to keep your car in top gear while climbing a hill. The higher the hill, the greater speed that’s needed. On the other side of the hill you make up for the fuel used to climb it.

    If you let cruise control take you up the hill, it will drop you down into lower gearing and rev up the engine in an effort to maintain the same speed (because that’s what you asked of it). It has no way of knowing that you are approaching a hill until you’re on it.

    The advice from Edmunds is correct – cruise on the flat and gentle grades, and use manual control on the hills.

    Here is my approach: use cruise until approaching a hill, then gently apply a bit more gas to gain speed for momentum to climb in top gear, letting off of the gas as I near the crest, then letting cruise control once again take over near the top. This approach keeps me in top gear and best fuel economy.

    Your advice about a speeding ticket is good. Keep your speed reasonable and don’t build it up too far in advance of the hill.

    Clair

  9. I’ll completely agree with marci. I have to do the same thing when I drive long distances. I get aggravated sometimes and just have to pass people.

    One other thing about fuel usage minimization while using cruise control is exactly what I stated above. You’ll notice yourself passing people less and doing the “accelerator shuffle” (i.e.- on and off the gas a lot) a lot less. This helps to maintain a steady flow of fuel. And at highway speeds, the engine is barely working so having a low and steady fuel flow means that you average out to using less of the stuff.

  10. Well cruise control did not help me…. I drove a 120mile trip and i had cruise control on and my tank was full and dropped to half tank. When i was coming back i did not use cruise control and i only used up a little more of 1/4 of my tank. And the trip i took did not have any hills.

    • How about wind direction ? I found 20 mph wind can make my Tacoma 20 mpg again it, 24 mpg on the trip following it. I had a 480 miles round trip to test it on the same day, at 65 mph, maybe a bit slower again wind.

  11. My experience with Cruise control are completely negative. I have a new Dodge Grand Caravan and I was getting about 9 km/l but when I used cruise I got about 6 km/l and I am very careful about my constant speed. So once again I changed my driving parameters and stopped using cruise control. Rather, now I use a different approach. On the downhill, I keep my car in neutral and it covers about 1 km without any effort and sometimes even 2 km depending on the traffic and other factors. So once again, I have been able to get about 9 km/l and believe that we should be keeping our cars in neutral on downhill.
    thanks.

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