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> Everybody knows that a modern car does not consume so much less fuel than a car of then comparable standard 20 years ago. Actually a modern car does consume

by jonknee 11y ago

> Everybody knows that a modern car does not consume so much less fuel than a car of then comparable standard 20 years ago. Actually a modern car does consume a lot less fuel than models from 20 years ago. CAFE standards have had a great effect. http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/html/table_04_23.html http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pub... For a new passenger car the average MPG in 1995 was 28.6 and in 2013 (latest available data for that report) was 36 MPG. That's a 25% increase which when multiplied across millions of vehicles is an enormous amount of fuel.

mhb 11y ago
It's a 20.6% decrease in gallons per mile.
- kazinator 11y ago
  That is misleading. We should calculate percentage improvements against the better value. Fewer gallons per mile is better. For instance, if you cut in half the gallons per mile, it only looks like a 50% decrease. But it's actually a doubling of the mileage: you go twice as far on a tank of gas. The improvement in gallons per mile is 100%. Using something other than mileage: suppose you optimize a program so it takes half the time to run. It's running twice as fast: it is 100% faster. Looking at it as a mere 50% reduction of time can be misleading. If you calculate the speedup using the running time, you have to divide the time difference by the smaller, better running time: 100 x (Tpoor - Timproved) / Timproved. The main problem with the "percent reduction" is that arbitrarily good improvements only approach 100%. If we make a car go a million times longer on a gallon of gas, it's only around a 99.9999 reduction in gallons per mile, which looks only about twice as good as a 50% reduction. :)
  - mhb 11y ago
    Suppose you're going on a 100 mile trip and you want to know how much better off you are if you replace your 50 mpg car with a 100 mpg car. You now only need 1 gallon of gas instead of 2. Even if the car can run without gas, you aren't any better off than a savings of 2 gallons for the trip. You're not > million times better off.
    - kazinator 11y ago
      I'm only not one million times better off because I have other costs to deal with which are completely unrelated to the gas. If the gas were the only resource I have to worry about (whatsoever), then I would in fact be a million times better off.
      - mhb 11y ago
        So if the 50 mpg car cost $5,000, you would be willing to pay >$5,000,000,000 for the 100 mpg car?
        kazinator 11y ago
        In fact, I understand economics well enough to recognize that I've already put more time and effort than necessary into this thread.
- jonknee 11y ago
  ... Which is a massive amount of saved fuel!

by jonknee 11y ago

mhb 11y ago

It's a 20.6% decrease in gallons per mile.

kazinator 11y ago
That is misleading. We should calculate percentage improvements against the better value. Fewer gallons per mile is better. For instance, if you cut in half the gallons per mile, it only looks like a 50% decrease. But it's actually a doubling of the mileage: you go twice as far on a tank of gas. The improvement in gallons per mile is 100%. Using something other than mileage: suppose you optimize a program so it takes half the time to run. It's running twice as fast: it is 100% faster. Looking at it as a mere 50% reduction of time can be misleading. If you calculate the speedup using the running time, you have to divide the time difference by the smaller, better running time: 100 x (Tpoor - Timproved) / Timproved. The main problem with the "percent reduction" is that arbitrarily good improvements only approach 100%. If we make a car go a million times longer on a gallon of gas, it's only around a 99.9999 reduction in gallons per mile, which looks only about twice as good as a 50% reduction. :)
- mhb 11y ago
  Suppose you're going on a 100 mile trip and you want to know how much better off you are if you replace your 50 mpg car with a 100 mpg car. You now only need 1 gallon of gas instead of 2. Even if the car can run without gas, you aren't any better off than a savings of 2 gallons for the trip. You're not > million times better off.
  - kazinator 11y ago
    I'm only not one million times better off because I have other costs to deal with which are completely unrelated to the gas. If the gas were the only resource I have to worry about (whatsoever), then I would in fact be a million times better off.
    - mhb 11y ago
      So if the 50 mpg car cost $5,000, you would be willing to pay >$5,000,000,000 for the 100 mpg car?
      - kazinator 11y ago
        In fact, I understand economics well enough to recognize that I've already put more time and effort than necessary into this thread.
jonknee 11y ago
... Which is a massive amount of saved fuel!