Raw data

For posterity, I thought I'd post the results from the beginning of my effort. You'll see the dates, miles and gallons for each fill up. Also, you'll see the cumulative days of the experiment and the standard deviation in mileage based on the results of each fill up. Note that no pre-experiment data exists, so you'll just have to take my word that the average mileage at that time was 14.9 m.p.g. based on the "average mileage" readout of the display unit in the car. I'd like to include graphs, but I haven't yet been able to figure out how publish them in a readable fashion. Sigh...

Date	Miles	Gallons to fill	Mileage	5-tank mov. Avg.
9/5/05	377.2	18.714	20.16
9/9/05	346.7	19.541	17.74
9/16/05	381.5	18.948	20.13
9/24/05	404.3	20.126	20.09
10/1/05	401.3	18.293	21.94	20.01
10/8/05	414.1	19.821	20.89	20.16
10/14/05	429.6	18.545	23.17	21.24
10/28/05	401.0	20.399	19.66	21.15
11/6/05	446.1	20.703	21.55	21.44
11/16/05	443.8	19.190	23.13	21.68
11/23/05	403.2	19.821	20.34	21.57
12/3/05	425.2	19.299	22.03	21.34
12/14/05	434.1	19.044	22.79	21.97
12/21/05	414.7	19.484	21.28	21.92
12/29/05	442.2	17.604	25.12	22.31
1/6/06	404.4	19.777	20.45	22.34
1/14/06	415.8	18.904	22.00	22.33
1/19/06	438.9	18.739	23.42	22.45
1/27/06	454.7	20.066	22.66	22.73
2/5/06	415.0	19.402	21.39	21.98
2/14/06	432.3	20.252	21.35	22.16
2/21/06	437.8	20.282	21.59	22.08
3/2/06	454.2	20.261	22.42	21.88
3/9/06	435.2	19.351	22.49	21.85
3/22/06	444.0	20.321	21.85	21.94
3/30/06	456.7	21.321	21.42	21.95
4/6/06	456.4	21.361	21.37	21.91
4/17/06	444.7	19.291	23.05	22.04
4/25/06	475.5	20.099	23.66	22.27
5/2/06	416.0	16.217	25.65	23.03
5/11/06	416.8	19.624	21.24	22.99
5/20/06	482.3	20.322	23.73	23.47
Totals:	13645.7	625.1	21.83
Standard deviation:		1.60	m.p.g.
Days of experiment:		257

Dilemma

I'm having trouble now deciding if I'm in the midst of an experiment or just trying to save all the gas possible. If it's the former there are several things I'd like to try, but I'm loathe to see the "average mileage" display creep down as I test hypotheses.

What hypotheses? The least likely to reduce my mileage has to do with fuel in the tank. I've always heard gas mileage is better during the first half of a full tank. The fuel gauges of all the vehicles I've owned act this way, but I suspect that that behavior is an artifact of the gauging mechanism. After all, half a tank weighs less than a full tank, and though the air doesn't know how much the car weighs so drag won't change, it does take more fuel to accelerate a heavier car. Further, increased weight adds to the tire loading, thus increasing road loads. I suppose it's possible that a larger hydraulic head in a full tank could somehow improve pumping efficiency but it seems far-fetched.

I'm a pilot, and I know from that avocation that fuel weighs about 6 pounds/gallon, so a full tank (21.5 gallons) in my car weighs about 129 pounds, the weight of an extra adolescent or perhaps female passenger. So it stands to reason that mileage would improve as fuel is used.

Finding out would take quite a while, filling and emptying to half a tank is not as exact as topping off to measure fuel usage. I'd fill to full, drive until I get as close as possible to, say, 5/8 full and refuel. I'd do this maybe 15 times, and calculate the mileage at each fill up. Then I'd drive down to 1/8 tank, add fuel to bring it to 1/2 full, drive down to 1/8, repeat, etc. Again, I'd do it maybe 15 times and compare. It wouldn't be exact because of the difficulty of filling and reading to exact level using the gauge but after sufficient trials, a conclusion should be possible.

Or perhaps the best way to measure this, since full tank is the easiest level to which to accurately fill, would be to run a series of trials, always filling the tank but alternating between using about 1/2 of a tank and close to a full tank. This way the accuracy of the miles per gallon achieved would be maximized, but the difference in the results would be minimized. Well, if I do the experiment I'll put a lot more thought into its design.

What else? I've achieved what I regard as a drastic reduction in fuel consumption by taking many different steps, as detailed elsewhere in this blog. Which of the measures are most effective and which are minor? Is it the slow acceleration that contributes the most, or perhaps the reduced freeway speed? The way to find out is to eliminate each measure I've taken, one at a time, and measure the result. Unfortunately, at least one or two of the experiments would likely lead to my having to watch the "average mileage" indicator show significantly deteriorating results, and I just hate to give back my hard won tenths of a mile per gallon.

Maybe I AM eccentric.

Proselytizing

In my previous post I expressed my skepticism that the U.S. would find the will to take even a significant portion of the measures I have undertaken to save gasoline. Part of my skepticism stems from a general feeling about "the way things go" and part from my experiences with friends, family and people at my company.

I've made no secret of my program. To some of the people I mentioned above saving something like $1,500.00 per year doesn't mean much. To others, it's a large amount, enough to make a difference in their lifestyle. But to a person, they all shake their heads and tell me they couldn't do it and explain to whomever is around that "Rob (I'm Rob) is eccentric."

A man who works at my company drives a big Ford dually pickup with a large diesel engine. He's put a chip in it to maximize performance and that sucka will most definitely hurry up. He commutes from Riverside, CA to Long Beach each day, a round trip I'd estimate at about 100 miles. He makes decent money but he just bought a house and at times is strapped.

I asked him today what it costs him to fill up and he told me $120.00. He's known from the outset of my experiment, he and I used to race each other. He's always just shaken his head about what I'm doing now, so I thought I'd present it to him and his buddy in a different way today. I said "you know Tim, driving this way I get the equivalent of every third tank of gas free." He acknowledged that that was an interesting way of looking at it, but it didn't change his behavior.

There was a song a while back called "I Can't Drive 55" by Sammy Hagar. I know that the vast majority of people feel that way and even with government action I don't see how people will adopt these habits. And as I mentioned in a previous post, I tend toward Libertarianism. So all in all, I'm probably tilting at windmills. But I'll continue to tilt at these and to look for others at which to tilt.

I think next I'll spend some time thinking about "unintended consequences."

Best case scenario

In my last post, I conservatively estimated that the U.S. would be able to immediately reduce its need for imported oil by about 5% by changing non-commercial driving technique in a mostly benign way. What about an optimistic yet not, in my opinion, pie in the sky estimate?

Well, I'm now at 22.7 m.p.g. in my 2000 Jeep Grand Cherokee Limited. The E.P.A. says I should get 15 m.p.h. city and 20 m.p.h. highway. I estimated in an earlier post that 36 out of every 60 miles I should be getting "highway mileage" and 24 out of every 60 miles I should be getting "city mileage." So a weighted average E.P.A. estimate for my driving regime would be (36/60)*20+(24/60)*15=18 m.p.g. But I've demonstrated that it's possible, with this driving regime, to get 22.7 m.p.g. at least.

Now, the vast majority of people to whom I've talked, about whom I've read, etc. complain that they don't achieve the E.P.A. estimates. Let's say the average is 90% of the E.P.A. estimate. I'm getting 126.1% of the E.P.A. estimate for my car. Suppose everyone went from 90% to 126.1% of the E.P.A. estimate. That would result in a 40.1% increase in gas mileage nationwide or a decrease to (1/1.401) times 100% = 71.4% of the fuel used before the change. That is, personal transportation fuel use would be reduced by 28.6%.

Using the figures in my previous post, that would result in a reduction of .286 times 6.4 Mbbl/day or 1.83 Mbbl/day. That's about 13.9% of our daily oil imports. Now we're getting someplace. All this without a single person driving a single mile less than they are currently driving or buying a more fuel efficient vehicle. And remember, this completely leaves out commercial use of transportation fuels.

Can it happen? Yes, of course. Look at the rationing during World War II. Will it happen? Probably not, but something much more onerous surely will.

So what?

OK, so I started this driving experiment in August 2005 and I've saved 15 tanks of fuel or so. What does that mean? It's a difficult subject. It's not likely to postpone the onset of the effects of so-called "peak oil," even if I could get everyone in the country to do it. A case can be made that, if everyone in the U.S. started driving the way I've driven during this experiment, it would have a very measurable effect on the need for imported oil. Alone, it wouldn't stop it but it would be significant.

But what would it accomplish? Well, reduction in the U.S. demand for imported oil would presumably lower the price or at least influence prices in a downward direction, thereby encouraging consumption in China, India, etc. Clearly, the path these "developing nations" are on is leading them to find plenty of ways to use oil, and a lower price would accelerate that process. Even so, I believe that huge advantages would still be gained for the United States.

Let's look at some numbers. It's not easy (for a layperson such as myself anyway) to find definitive numbers for some of this, but I've given it my best shot. Should anyone have better information, I would welcome it.

Of the approximately 20.5 Megabarrels/day (Mbbl/day) of oil used in the U.S., about 13.7 Mbbl/day goes to transportation. As best I can determine, something like half of that, or 6.4 Mbbl/day goes to "non-commercial" transportation. This is where I make my impact. Suppose all the drivers in the U.S. took the "realistic" approach I mentioned in my first posting in this blog and that my estimates are correct. I had felt that a 15% gain in average fuel economy was reasonably achievable, but let's be more conservative. I believe that 10%, or .64 Mbbl/day could easily be saved. That amounts to about 5% of our oil imports.

What??!! Reducing speed from 70 m.p.h. to 55 m.p.h., avoiding drive-through windows and other unnecessary idling, judicious use of the gas pedal, etc. is only good for a 5% reduction in import demand? And EVERYONE would have to do it?? Well, it is one of many relatively painless steps that can be taken.

Suppose we really wanted to end our dependence on oil imports. If, instead of increasing our oil consumption annually, we reduced it by 5%, we would eliminate our dependence in 18 years. This assumes that U.S. petroleum production remains constant.

Of course, the reduction attained by conservative driving techniques represents 5% of imports, not 5% of consumption. So that, along with some other measure, would be the steps to be taken on the first of the 18 years. They only get harder after that.

I've carefully avoided controversial political aspects of oil use. In particular, I've brought up neither "peak oil" nor "greenhouse emissions" in this blog prior to this post. I started my experiment simply as a way to see how much gas (and money) I could save and at what cost in terms of frustration. The answer is that I can save about 500 gallons or over $1,500.00 per year. And though I've experienced very little frustration, I suspect I have frustrated some of those who have ridden with me and I'm certain that I've frustrated some of my fellow drivers.

Still, I believe that this is important. It has genuinely changed my outlook on my energy budget. I have become much more aware of my personal "energy leaks" and the leaks of my business and those around me. Much more will be required, but I won't dismiss the value of this small experiment in efficiency.

Use of time

One of the problems of maintaining a maximum speed of 55 m.p.h. is that it seems to waste a lot of time. Of course, use of the mobile phone, listening to books on tape, etc. can make this time less unproductive than it might seem at first. But it's a constant challenge to find ways to be productive during commutes, whether on a professional basis (phone conversations with business associates, etc.) or a personal basis (books on tape).



But what about the time itself? How much is actually lost? I drive about 60 miles per day on average, I estimate that 36 of those miles are spent driving at 55 m.p.h. when I could drive 70 m.p.h. That's faster than the speed limit but probably about what would be considered "normal." At 55 m.p.h. I spend 39 minutes, 16 seconds driving more slowly than "normal." If I were driving at 70, I would spend 30 minutes, 51 seconds driving the 36 miles. So I seemingly lose 8 minutes, 25 seconds per day.



However, I also only have to refuel about every 8 days instead of every 5.3 days (on average). I estimate that pulling off the road, fueling and getting back on the road takes about 8 minutes, so I save an average of 31 seconds per day stopping for fuel less often. Thus, the grand total loss is 7 minutes 54 seconds per day. In the course of a year, I lose 33 hours and 11 minutes behind the wheel (assuming 252 such days per year).



Looking at this time another way, my company values the 7 minutes and 54 seconds at about $12.66. An interesting comparison is that, on a given day, I save about 1.4 gallons of fuel compared to what I would have consumed using my pre-experiment driving style, which, at current Southern California prices, is worth about $4.57.



Or, yet another way is that I try to sleep 7 hours per night. Thus, the extra time spent driving amounts to 0.77% of my waking hours.



Hmmm....

Ween us from imported oil? Maybe not...

One of the things I've done in my quest to get the maximum out of a tank of gas is to forgo the drive-through window. In so doing, I began to wonder how much gasoline is burned in the United States idling at drive-through windows. I decided to try to figure it out - maybe outlawing drive-through windows (something a person with a libertarian bent such as myself would never advocate) would end our reliance on imported oil.

I've read that Enrico Fermi felt his students should be able to come up with an estimate for almost anything. The classic example is to estimate how many piano tuners there are in New York City. There's even a competition to come up with order of magnitude estimates ("Fermi Answers") to obscure questions. Though I've never entered any sort of formal competition of this nature, the idea fascinates me. Anyway, such skills helped me with my answer to the query mentioned above.

Though "google is my friend," I wasn't able to find every piece of data I needed in my fairly brief search. I couldn't find statistics on how many fast food drive-through window visits occur in the U.S. in a day (or a year). Using estimates based on how many drive-through windows I think there might be, how often the people I know use them, what I've seen at the restaurants, etc. I decided maybe 1.5 million such visits occur each day. I estimated that an average visit is four minutes, and an average car burns 0.25 gallons per hour at idle (mine burns 0.38). I subtracted a minute because that was my guess as to the idling equivalent of pulling into a parking space, stopping and then starting the car after going into the restaurant.

Using these figures, I estimate that 18,750 gallons of fuel are wasted in drive-through window visits per day in the U.S., or about 6.84 million gallons per year. I was able to find a very informative site from a consulting geoscientist. I learned that a barrel of oil produces 19.5 gallons of fuel, so 6.84 million gallons require 350,000 barrels of oil.

I also learned that we use 21.93 million barrels PER DAY of which 13.21 million barrels are imported. So we import 4.82 billion barrels of oil per year. Thus, elimination of all fast food drive-through window stops could eliminate maybe .007% (that is, 7 one-thousandths of 1%) of our oil imports.

Well, ya gotta start somewhere...

To floor it or not to floor it

I'm trying to understand the effects of rate of acceleration on minimizing fuel consumption over a given distance. We've all read and heard that "jackrabbit starts" waste fuel. How can this be shown? Well, fuel contains energy in hydrogen and carbon chemical bonds. We oxidize fuel to release this energy. The energy does two things in our vehicle - it adds kinetic energy, thus changing the potential energy of the chemical bonds to the kinetic energy of the moving vehicle, and it does the work of moving the car against the sum of the forces acting to resist motion. These include engine and driveline friction, pumping fluids, aerodynamic drag, tire rolling resistance, etc. For the purists, it also can increase our potential energy by utilizing chemical potential energy to raise our position in the Earth's gravitational field (i.e., take us up hills). But since, on average, our vehicle stays at one elevation (that is, at the elevation of wherever it lives) we can ignore this.

It's easy to show that the more slowly we accelerate, the farther we go in the process of adding a given amount of kinetic energy to the car (that is, getting up to a given speed since kinetic energy is one half the product of the mass of the vehicle and its contents times the square of the velocity or speed). Thus, if we accelerate from 0 to 60 in twice the time, that is, accelerate at half the rate, we will go twice as far to add the same amount of kinetic energy, which comes from burning the fuel. So, the same amount of fuel will take us twice as far while getting us up to the same speed. It will take longer but be more fuel efficient. As I said, this is quite easy to show mathematically.

So it seems like a no-brainer. But... It's also true that there is a speed at which an automobile gets the best fuel economy. Because it burns fuel while idling (my Grand Cherokee burns 0.38 gal/hour as nearly as I can determine), the car gets 0 m.p.g. standing still. As we start moving and achieve higher speeds the fuel economy, that is, the m.p.g., increases. Above some speed, different for each vehicle, the aerodynamic drag, which increases approximately with the square (at least according to my calculations - others say cube) of speed begins to take its toll and the efficiency decreases. So, the vehicle is more efficient (gets better gas mileage) the faster you go, up to some speed at which efficiency begins to decrease. I'm still working on the mathematics of this but it seems intuitively reasonable and agrees with the nuggets I've found on the web (see here for example) and some "back of the envelope" calculations.

So let's say, for conversation's sake, that for my Grand Cherokee, the most efficient speed is 50 m.p.h. I think this isn't too far off, based on my experiments and a website I found (but since lost). And let's say I'm going to take a 20 mile trip. To make it easy, the trip is on a level road, no stops. I could, in principle, accelerate so slowly that I don't get to 50 m.p.h. before reaching my destination. Or, I could floor it and reach 50 m.p.h. as quickly as possible and drive the greatest possible portion of my trip at the most efficient speed. So flooring it gives me the maximum number of miles at the most efficient speed. On the other hand I could, in principle, accelerate so slowly that I only get to, say, 5 m.p.h. before reaching my destination and drive the entire trip at a very inefficient speed. This seems to imply that quick acceleration is most efficient. So which is best?

I'm still working on it, so more to follow.....

The Goal

I'd like to welcome myself to the world of blogging. I have a hard time with the term "blogos.....," maybe in time I'll come to accept it.

The intent of the blog, in the beginning, will be to document my efforts to minimize my use of energy, particularly auto gas. I drive a 2000 Jeep Grand Cherokee Limited with a 235 horsepower V8.

Until August of 2005, I drove it like I used to drive my 1970 Roadrunner in high school, that is, as fast as traffic would allow (and sometimes faster). As for acceleration, I used to say "I don't need an accelerator pedal, I just need a switch." It was full throttle all the time. The Jeep is equipped with a display of "average mileage" and "instant mileage." As nearly as I can tell, the average represents mileage over the last several tanks - maybe 4000 or 5000 miles. It can't be from 0 on the odometer - it changes too quickly for that. Or so I think.

In any case, at the start of my experiment, the average m.p.g. was 14.9, reflecting my extreme driving habits (according to the E.P.A. the car is rated for 15 m.p.g. city, 20 m.p.g. highway).

In August of last year, as gas prices in the Los Angeles area approached $3.00 per gallon, I started toward the opposite extreme of driving, incorporating snail-like acceleration, coasting down hills in neutral, shutting the engine off at long stops, cruise-controlled 55 m.p.h. and attempts to look ahead and put the car in neutral to coast to a stop for traffic, etc. The brake pedal became my enemy, I pictured burning gasoline to heat chunks of metal. I filled my tires to 2 p.s.i. over the maximum rating (don't try this at home).

My current average is 22.5 m.p.g., a 51% increase. I estimate that I have saved approximately 350 gallons of fuel. Obviously, someone starting from a more normal driving technique could not expect as great an improvement. But even for someone getting average mileage consistent with the EPA estimate, say 18 m.p.g., which many do not achieve, a 25% improvement would be possible. Again, most would not take it to the other extreme as I have, but a 15% improvement would seem to be easily achievable.