Friday, June 20, 2008
Miles-Per-Gallon Math
When a 2-miles-per-gallon improvement is better than improving by 16 miles per gallon.
By Kevin Bullis
Say you've got two cars in your garage. One of them gets 34
miles per gallon; the other gets only 12. You drive both cars 10,000 miles in
the course of a year.
Would you save more gas by a) trading in the 34-miles-per-gallon
car for one that gets 50 miles per gallon, or by b) trading in the 12-miles-per-gallon
car for one that gets 14 miles per gallon?
New
experiments suggest that people tend to pick a). After all, a 16-miles-per-gallon
improvement seems better than an improvement of just 2 miles per gallon.
The right answer is b).
If you start driving the 50-miles-per-gallon car instead of
the 34-miles-per-gallon car, you'll save 94.1 gallons of gas per year.
If you start driving the 14-miles-per-gallon car instead of
the 12-miles-per-gallon car, you'll save 119 gallons per year.
The math is simple arithmetic. Divide the total number of
miles driven (10,000) by the miles per gallon to get the total gallons used to
drive that distance. For 12 miles per gallon, the answer is 833. For 14 miles
per gallon, it's 714.
The fact that people guess a) rather than b) suggests that
miles per gallon isn't a useful metric for describing a vehicle's gas
consumption, say the researchers who did the recent experiments. A much more
direct way to measure fuel consumption is an estimate of the amount of gas required
to travel a given distance.
Such a number would also make it easier to convey just how
much could be saved by moving closer to work or taking public transportation.
And it renders the difference between a 12-miles-per-gallon SUV and a 50-miles-per-gallon
hybrid more impressive, making it clear just how much fuel gas guzzlers are using.
It takes 833 gallons to travel 10,000 miles in the former vehicle; it only
takes 200 gallons to go 10,000 miles in the latter.
Massachusetts Institute of Technology
Comments
Flip
06/23/2008
Posts:18
Barry G.
alerion
06/23/2008
Posts:1
tplum@plumha...
06/23/2008
Posts:1
blunney
06/23/2008
Posts:17
"miles-per-hundred-gallons."
I assume you mean '100-miles-per-gallon' on that one?
Manuvidya
08/22/2008
Posts:19
rwmiller1017
09/03/2008
Posts:1
It's a contrived scenario design to illustrate a point - albeit poorly - that the greatest impact, (financial, environmental or otherwise) comes from using LESS gas in total, rather than using less gas relative to what you're using today. In fact, the right answers are then a) ride your bike or, (possibly more practically) b) telecommute whenever you can.
Since not everyone's ready to wedge the kids into a fuel sipping hybrid for an 8-hour drive to Grandma's house, we should be encouraging people to select the most fuel efficient method to accomplish their objective...if there's an option to avoid using gas, take it - if you're commuting on your own, use the smaller fuel sipping option - if you've done your absolute best to pack lightly but still need the extra space, use the smallest,(which usually correlated with the most fuel efficient) Crossover/SUV that meets your needs. Realistically, that strategy has a better chance of creating the desired impact of less gas usage overall...
rhutzul
06/23/2008
Posts:3
Thanks, Clint
porosity
06/23/2008
Posts:3
mkogrady
06/25/2008
Posts:206
Uhhh, are you a taxpayer?
After whatever period / amount of initial subsidy, if even truly necessary, quit sticking it to the taxpayer. Rachet the subsidy (and fuel content mandates) back down to 0.
Ethanol *FROM CORN*, has proved to be a horribly uneconomic method of capturing solar energy. Higher taxes, higher corn / food prices, higher gasoline prices, lower BTU per gallon (thus MPG) of gas(ahol). Makes no economic sense, at all.
Corn now at $7 / bushel, versus fluctuating, for a very long time, between $2 and $3.
nekote
07/08/2008
Posts:139
A number of comments have suggested some form of 'gallons/mile' measure. The report Study questions method of listing fuel efficiency supports this idea. At the risk of bringing bad bad memories of 'lowest common demoninators', it is easier to compare two values if the 'per x' value is the same. Miles per gallon is useful in estimating distance given a similar volume of fuel. Gallons per mile is better when trying to estimate the fuel used over a similar amount of distance.
In the example above, 12 mpg and 14 mpg are roughly 8.3 g/100miles and 7.1 g/100miles, an improvement of 1.2 g/100miles. In comparison, 34 mpg and 50 mpg are roughly 2.9 g/100miles and 2.0 g/100miles, an improvement of 0.9 g/100miles. It all depends what you are trying to achieve.
nh
06/23/2008
Posts:3
A “COMMON” standard measurement of “Energy Units per Distance Traveled (EU/DT) could be the base, and since the "EU" will be comprised of 8 to 12 or more products, the "DT" has to be one standard…..(I say 100 mi.)” so that the “$ cost per Distance Traveled” which is what consumers need to know can always be determined “with grade 5 math”
So the near future requires a change in terminology from MPG to EU/DT (EU/100mi) so we can easily determine our “$/100Mi” for the car we own or plan to buy.
We now say "my car GETS 25 Miles per gallon.”
We should say "my car USES 4 gal. per 100mi.”
Assuming $4.00 gas we should say “my car COSTS $16.00 per 100mi. to operate” or $16/100mi.
We might someday soon say “my car USES ?? KWH per 100mi” and from that the cost is easy to determine.
With this change in terminology, no matter what source of energy you choose the comparison will always be "apples to apples" when determining the REAL value/cost of "$/100mi"
I have used KWH as a unit for electrical measurement because I have no idea how “electric units of energy” will be measured, or what those units will be called. Anyone??????
xxxander1
07/22/2008
Posts:2
Brian H
08/21/2008
Posts:28
For me the take-away is a simple rule of thumb: Upgrade your worst efficiency machines (of any kind) before you upgrade the most efficient. This is also intuitive for most people along the lines of, "I'm happy with my fuel-efficient car; I want to replace my gas guzzler."
In fact the best solution to your question would be to replace the 12-mpg car with the 50-mpg car. Most people would do that rather than limit their choices to the two you gave as an illustration. But still, it illustrated a good point.
MakeSense
06/26/2008
Posts:93
Uncertainty in the price of oil is an important factor in determining what kind of car people buy these days.
energymv
07/01/2008
Posts:19
An economic measuring stick ($/mile) or energy measuring stick (miles/KWH; miles/BTU) would be better, IMHO, than the widely used MPG (Miles Per Gallon).
Maybe the inverses (mi/$, KWH/mi, BTU/mi) would be preferable?
nekote
07/08/2008
Posts:139
The U.S, should use “Gal. per 100 mi. (or per 1000 mi.) which makes the REAL value “$ per 100 Mi” easy to figure with "grade 5 math". Of course it would follow then to use, as needed, “KWH per 100 mi.” as well as “BTU per 100 mi.” or "????", each as easy to convert to the IMPORTANT measure of “$ per 100 mi” (in short: Gallons per 100 mi. not miles per gallon)
The only economic question that holds any relevance is after all “$ per 100 mi” (or $ per 1000 mi. or $ per 100 kilometre). And why is this important, well let’s just take one “alternate fuel” E85,
which doesn’t deliver the same power as gas and requires more gal. per 100 mi than gas does, so now try to find the $/100mi cost the old way.
However this would require the Government, the Auto Manufacturers and the Schools to agree to a “COMMON” standard measurement of “Energy Units per Distance Traveled (EU/DT) and since the "EU" will be comprised of 8 to 12 or more products, the "DT" has to be one standard…..(I say 100 mi.)” so that the “$ cost per Distance Traveled” which is what consumers need to know can always be determined “with grade 5 math” So the near future requires a change in terminology from MPG to EU/DT (EU/100mi) so we can easily determine our “$/100Mi” for the car we own or plan to buy.
We now say "my car GETS 25 Miles per gallon.
We should say "my car USES 4 gal. per 100mi.
With this change in terminology, no matter what source of energy you choose the comparison will always be "apples to apples" when determining the REAL value 0f "$/100mi"
xxxander1
07/22/2008
Posts:2
lasertekk
07/20/2008
Posts:78
davidb@mcbd....
07/28/2008
Posts:1
Why spend all of the natural resources (Steel, platinum, coal, etc.) to build a slightly more fuel-efficient vehicle for this person to buy and then sell the currently owned vehicle to someone else to drive? Plus, if the vehicle is relatively new, you're likely going to lose major money on the resale.
Did a car company come up with that question? It sure sounds like it to me.
justahick
08/31/2008
Posts:11
MickeyFouse
11/25/2008
Posts:47