The mpg confusion

[one...two...tree 2,762]

What reduces emissions more?

A. Someone swapping their old SUV (which gets 12 miles per gallon) for a hybrid version (18 mpg) or

B. someone upgrading their 25 mpg compact to a new 46 mpg Prius?

(ignore for a minute manufacturing issues or driving habits and assume the miles driven are the same).

The surprising answer (for those who don't work it out) is A. It's easy enough to see why this is the case. If the driving distance is 100 miles, then for case A the saving in fuel used (and hence emissions) is 100/12-100/18 = 2.8 gallons, while for B, you have 100/25-100/46 = 1.8 gallons. The confusion arises because people like to think linearly about numbers, not inversely, and so tend to assume that a similar change in mpg has a similar impact on fuel usage. This is not however the case - improvements in efficiency at the low end of the scale are much more useful at reducing emissions. This is actually a very general point - when trying to raise efficiency it is always sensible to start with the least efficient processes.

This confusion got some attention a couple of months ago after a piece that was published in Science by Larrick and Soll. They tested peoples instinctive reactions to changes in mpg numbers and found that people very often got it wrong, leading to less than optimal decisions. They also tested a different way of giving fuel usage information (the number of gallons used per mile), and since this is linear in emissions, people made the correct judgment much more often (it's worth noting that the standard in most of Europe is already litres per 100 km). Rewritten in those terms, the choices above become:

A. Someone swapping their old SUV (which takes 8.3 gallons to go 100 miles) for a hybrid version (5.6 gallons/100 miles) or

B. someone upgrading their 4 gallons/100 miles compact to a new 2.2 gallons/100 mile Prius?

Much easier, right? The authors of the Science piece are trying hard to get US manufacturers and the EPA to switch over from mpg to this new standard (though they prefer gallons/10,000 miles). It all seems eminently sensible to us.

http://www.realclimate.org/index.php/archi...-mpg-confusion/

[Pinocchio Liberal 268]

Go mow the yard, do dishes,vacumn. sheesh!

[VisaJourneyLady 33]

the answer is C, change from an old SUV they didn't need to a more fuel efficent car (30 or more mpg). American's obsession with SUV's is sadly a disease that's spreading around the globe. Most people don't need them. SUV's are DUMB.

[IAMX 3,055]

I don't see what people's problem with SUV's are, beyond the gas guzzling aspect, which any logical person would have a problem with. I personally like SUV's, particularly 5 seaters, which is enough for a family, because vans are just too damn big, we're not going to have 5 kids, and vans aren't exactly gas savers themselves.

However, the emissions per mpg thing does make sense on the lower scale because those with relatively high MPGs going even higher are already very low polluters. It's the high polluters whose emissions tests gets bumped up most dramatically from that small increase.

Thing is, you still have to be retarded to buy an 18MPG SUV. There are already hybrid SUVs out there that get 30.

http://www.fueleconomy.gov/feg/sbs.htm

2008 Ford Escape Hybrid (FWD): 34 City, 30 Hwy, 32 Combined (2009 Similar)

2008 Ford Escape Hybrid (4WD): 29 City, 27 Hwy, 28 Combined (2009 Similar)

2009 Mazda Tribute Hybrid (FWD): 34 City, 31 Hwy, 32 Combined

2009 Mercury Mariner Hybrid (FWD): 34 City, 31 Hwy, 32 Combined

For the 2008 model Ford Escape, moving from standard petrol/ICE with no hybrid, to hybrid electric/ICE, the mileage increased by 8mpg, reduced carbon footprint over 30%, and on a 10-scale EPA air pollution score, increased from 6 to 8, higher being better.

Now, the stupid a$$'s hybrid comparison which does nothing on emissions goes to the 2008 GMC Yukon XL. Yukons are very well selling SUV's, are way too big, and are like the short man's large truck, or so is my view, and I intend on keeping it. So in this wise purchase of a non-hybrid Yukon you get 14 City, 19 Hwy, 16 combined. With the hybrid version, you get 21 City, 22 Hwy, 21 Combined, 20% reduced carbon footprint, and no change whatsoever in air pollution.

The wise choices are out there, just gotta convince people to stop being idiots.

[spookyturtle 9,466]

Most people don't need them. SUV's are DUMB.

But for the people that do need them, they aren't dumb, they are a necessity. Ever tow a trailer with a Prius?

IThe wise choices are out there, just gotta convince people to stop being idiots.

It must be tough being you, huh? Everyone is an idiot in your book.

[IAMX 3,055]

It must be tough being you, huh? Everyone is an idiot in your book.

Only people who make fun of others or look down on others for having an econo-car and down the road pay for it. If that's "everyone", then everyone is an idiot. However, that's not the case, so lets stick to that.