An interesting article on the new scientist website today. They have some researchers arguing that presenting fuel efficiency in miles per gallon confounds decisions on how to improve overall fuel consumption.
Their argument is very simple. An increase of 3 miles per gallon on a vehicle sounds insignificant, and on an already fairly fuel-efficient car it would be. However, they point out that on a very sure inefficient vehicle, and this might actually be extremely worthwhile.
Once fuel economy is expressed in gallons used per unit of distance, then it becomes much more obvious what a sensible decision would be when trying to focus on overall fuel savings. Unfortunately for the petrol head, it becomes clear extremely quickly that focusing on even apparently very small improvements in efficiency on very thirsty vehicles is far more worthwhile van with large improvements on already efficient vehicles.
I thought this was both obvious, but also strangely interesting in how counterintuitive this is in some ways.
Article and related video here:
tinyurl.com/4xduwt
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The article is headed "Scrapping 'mpg' could boost sales of greener cars", but what percentage of car buyers select their next car on the basis of its "greenness"? Very very few, I would imagine. In fact a lot of buyers seem to be more swayed by things as trivial as the looks and the body colour than by the car's specification.
Edited by L'escargot on 20/06/2008 at 13:28
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Essentially the question was, "You have a 15mpg 4x4 and a 34mpg family saloon. You want to reduce your fuel use. Your options are to change the 4x4 for a 19mpg model, OR change the family car for a 44mpg model. Which do you choose?"
While it's an interesting academic point that fewer people got the wrong answer when mpg was replaced with gals per 100 miles, I'm not sure how relevant it is to real car sales. If you have decided you want a 4x4, you have presumably already ruled out family saloons. And one of the factors you care about its fuel efficiency, 15mpg vs 19mpg tells you which 4x4 is better and you have no interest in the fuel consumption of family saloons. Similarly, if you have decided you want a normal family car and you don't want a 4x4, 34mpg vs 44mpg tells you the same.
If there happen to be people out there who own both a 4x4 and a family car (or any two significantly different classes of vehicle), who are in a position to and are looking to replace just one of them with saving fuel being the most important criterion, and who fall into the group likely to get the arithmetic wrong if economy is measured in mpg, then perhaps they might benefit. But how many people does that cover?
Persoanlly I don't care what units are used to measure fuel consumption - I think I am mathematically literate enough to cope. But I don't see the suggested change being much of a silver bullet.
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I didn't think that was the main point being made.
Simply considering it as an exercise to make the oil last longer (and to reduce fuel bills), you're better off making what look like small improvements in efficiency in thirsty cars than you are making 'large' improvements in cars that weren't too bad in the first place.
I think that's relevant to both consumers (present it as a much larger cash saving than the headline mpg would indicate to them) and governments. If measures like BMW's simple changes can save 3 mpg, then that's actually a big deal for a lot of thirsty vehicles out there, and presented in cash terms, might influence people's thinking. There's a lot of people noticing the sting at the pumps at the moment.
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I still don't see how it would have much effect on someone buying a car. The conclusions is that, while going from 34 to 44 mpg might sound better than going from 15 to 19, the first one actually only saves 0.7 gallons per 100 miles, but the second one saves 1.4. That is interesting, and it may well be counter-intuitive to many people at first - I just don't see it being any more helpful to an individual's car purchase decisions than quoting mpg.
If you're in the showroom contemplating your next SUV purchase, is 5.3 gal/100 miles vs 6.7 gal/100 miles likely to be any more persuasive than 19 mpg vs 15 mpg? If you don't bother to do the sums, you just see that one number is a bit better than the other. If you do do the sums, it's a 21% improvement whichever units you use.
The only thing I can imagine being direct enough to have an effect is to quote, as you suggest, in cash terms: pence per mile (or £ per 100 miles), for which, of course, you have to assume a particular fuel price. I would imagine that that is the most direct way of describing it for most people. I think £29 per 100 miles vs £36 per 100 miles means something to everyone - it's certainly the only number I really care about.
If you don't have that number, you have to do some arithmetic to get it. I expect most people don't do the arithmetic. But for those that do, once you've decided you're happy with the idea of doing some sums, getting to £ per 100 miles from mpg is hardly more effort than getting there from gallons per 100 miles.
You're right about the big picture - across the industry it's worth knowing that there is more to be gained by adding a few mpg to the thirsty vehicles than by adding several mpg to the frugal ones. But I expect the people whose job it is to worry about that level of strategy already knew that.
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The only thing I can imagine being direct enough to have an effect is to quote as you suggest in cash terms: pence per mile (or £ per 100 miles) for which of course you have to assume a particular fuel price. I would imagine that that is the most direct way of describing it for most people. I think £29 per 100 miles vs £36 per 100 miles means something to everyone - it's certainly the only number I really care about.
I think you are spot on. People care more about money than MPG or CO figures.
once petrol gets expensive people will start to pay attention to MPG figures rather than the latest bling attachements.
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The fuel gauge was broken on an old car I had some years ago, but I knew it did roughly 30mpg and petrol was about £2 per gallon so when I put, say, £10 in and set the trip meter to zero, I knew I was ok for about at least 150 miles. I don't recall that the then expense seemed worse when computed in this way and £2 a gallon wasn't cheap in terms of my then income.
As someone said, there are many more factors in car purchase than economy or doing the least possible damage to the planet. I don't think people would bother to contribute to this forum if economy was all that mattered where cars are concerned.
Cars are about a lot more than transport. They can be fun. They can represent success. They can present a challenge. We know that the government sponsored figures on economy relate little to the real world. But you still get people on here wondering if they can reject a car which doesn't live up to the "official" figures.
I drove a friend's Merc 380SL on a few occasions years ago and it had a sort of rainbow coloured dial that showed whether you were driving economically or burning the fuel: the further into the darker colours the needle went, the more you used. I liked it because you could enjoy yourself and the car, keep the needle in the red for a while, and then cut back a bit. I think something like that would be worth having because of the immediacy, rather than an electronic gizmo that works out averages since re-set or whatever.
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