Thanks for the reply. I'll have to think about it more, but I don't think I agree with this argument. There appears to be a subtle logical flaw here. Namely, I'm not sure the concept of "fleet average fuel efficiency" is useful, using either form of averaging.
Averaging the km/L of several vehicles gives you the average number of miles traveled if we restrict all of the vehicles to use the same amount of gas. Averaging the L/100 km (or L/Mm if you prefer) of several vehicles gives you the average volume of gas consumed if we restrict all of the vehicles to travel the same distance. If the vehicles travel different distances and use different amounts of fuel, neither "average" would be useful in determining either the fuel consumed or the distance traveled, at least using any formula I can think of. You certainly can't just average the distance traveled and multiply by the average L/100 km. That would give you a meaningless number. In almost any case in which we are dealing with vehicles with vastly different fuel consumption, I would think that the distances traveled per vehicle would be uncorrelated with one another. Therefore, if "average fuel efficiency" has somehow made it into our law, then it is that useless concept itself which should be jettisoned. And indeed the L/100 km average is precisely as misleading as the km/L average, though in a different way. By all means, correct me if I'm wrong. --- "J. Ward" <[EMAIL PROTECTED]> wrote: > The biggest disadvantage of km/L is to give a huge loop-hole to auto > maker who sell gas guzzlers. For example, the U.S. government has > requirements for fleet averages in terms of miles/gallon. Imagine I'm > an automaker and I want to sell muscle cars or monster trucks that > average 5 miles/gallon. If I can sell a single 55 mpg economy car for > every 5 mpg gas-hog I sell to get a respectable fleet average of 30 > mpg. This misleads the public (and most Congressmen!) into assuming > that the cars sold use the same amount of fuel to go a given distance as > two vehicles that individually average 30 mpg. Nothing could be further > from the truth! In fact, the two vehicles use the same amount of fuel > to go a given distance as two vehicles that individually average 9 mpg. > > Now work the same problem in L/100 km. The economy car uses 4.3 L/100 > km. The guzzler uses 47 km/100 L. The fleet average is 26 L/100 km, > which accurately reflects the huge amount of fuel used by the fleet per > kilometer driven. Clearly, Europe is doing a lot better than we are in > terms of how they measure fuel consumption. > > Finally, I would add that an SI purist would never use km/L. As a > physicist I would speak in terms of "per meter squared." > > Therefore, I prefer L/100 km over km/L, clumsy as it may seem at first > glance. > > J. > > Bill Potts wrote: > > >Clearly, km/L is the more rational. > > > >Bill Potts > >Roseville, CA > >http://metric1.org [SI Navigator] > > > >-----Original Message----- > >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf > >Of Ziser, Jesse > >Sent: Sunday, January 27, 2008 17:38 > >To: U.S. Metric Association > >Subject: [USMA:40252] Re: convenient numerical values > > > > > >--- Pat Naughtin <[EMAIL PROTECTED]> wrote: > > > > > > > >>On 2008/01/28, at 8:10 AM, <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> wrote: > >> > >> > >>>Deciliter in the denominator is conventional medical practice in > >>>which "convenient numerical values" are considered more valuable > >>>than coherence of units. The same is true for grams and mg in > >>>medical practice. > >>> > >>>Gene. > >>> > >>> > >>> > >>Dear Gene and All, > >> > >>The expression you use here, 'convenient numerical values' appears > >>quite often in many different contexts and, it seems to me, that this > >>is at the expense of an efficient metrication upgrade. > >> > >>Another example is the change from millibars to hectopascals in > >>meteorology where the numbers stay the same while the unit name > >>changes without gaining the benefits of the coherence of the metric > >>system or the convenience of the 'rule of thousands'. I am sure that > >>there are many other examples. > >> > >> > > > >I'd like to offer another possible example of violation of the rule of > >thousands. I keep seeing L/100 km in fuel efficiency contexts. I also > >occasionally see km/L but it appears to be rarer. > >km/L is clearly more "thousandy", and also has the debatable advantage of > >being "distance per volume" just like MPG. Besides, "L/100 km" seems an > >awkward mouthful. Is this really the preferred unit? > > > >I'm thinking about getting metric mileage bumper stickers for my friends and > >family (most of whom I'm sure would enthusiastically accept and display > >them) and I was wondering if anyone had any other opinions on the km/L > >versus L/100 km issue. I've been unable to find much about it online. > > > >Thanks. > > > > > > > > > >____________________________________________________________________________ > >________ > >Be a better friend, newshound, and > >know-it-all with Yahoo! Mobile. Try it now. > >http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ > > > > > > > > > > ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
