pash wrote:I wrote this on another site in the course of a discussion of
a blog post on how the "miles per gallon" metric of fuel efficiency is misleading:
A poorly written post on a subject that is surprisingly intriguing when better elucidated. A
study published in Science several years ago does that (sort of). The study found a systematic misinterpretation of the miles-per-gallon metric in the sense that participants consistently overvalued vehicles with high MPG ratings. They assigned values linear in MPG rather than linear in its inverse.
The study's authors asked participants to "assume you drive 10,000 miles per year for work, and this total amount cannot be changed." The participants were then to come up with values for vehicles of varying fuel-efficiencies. That is indeed the sort of optimization problem people are faced with when buying a car, and clearly a fuel-efficiency metric that puts the amount of fuel in the numerator makes the problem easier to solve [1] because expenditure is proportional to amount of fuel when distance driven is taken as given.
But in reading the article, what most stood out to me was the lack of attention paid to the "miles" part of the equation. Taking distance driven as fixed is surely an enormous detriment to the goal of reducing carbon emissions in America. Yes, reordering your daily life to drive fewer miles is more disruptive than simply buying a more fuel-effiecient car. And, granted, once you've chosen your lifestyle, minimizing the amount of gas you burn as you go about your daily routine is a sensible step. All the same, it's ludicrous to ignore the basic inefficiency of the suburban style of life that dominates in this country while we wait for automotive engineers to come up with something clever to save us from pricey gas and carbon emissions that are twice as high per capita as many other countries at a similar level of economic development. Surely living closer to where you work, using mass transit, biking, and walking more must be part of the solution as well.
1. As the study shows, people at large are very bad at math.
There was a recent "Car Stuff" podcast on MPG vs. GP100M (Gallons Per 100 Miles) and how using GP100M would do a lot more to accurately convey fuel savings when considering a new car. There example was: You family has a sedan and a SUV. The sedan gets 25 mpg and you can trade it in on a sedan that gets 50 mpg; your SUV gets 10 mpg and you can trade it in on a SUV that gets 20 mpg. (lets assume there are legitimate reasons for having a SUV) Which is the better move?
With the SUV you go from 10 GP100M to 5 GP100M for a net savings of 5 GP100M.
With the Sedan you go from 4 GP100M to 2 GP100M for a net savings of 2 GP100M.
So the SUV is the smarter unit to replace as you will realize 2.5 times greater efficiency over upgrading the sedan.
This is why the T. Boone Pickens idea to retrofit all of the Semis to run on natural gas and initiatives like Cash for Clunkers are the best first steps in lowering overall fuel consumption. Get the worst offenders off the road first.
Does anyone know if the railroads are using any type of Bio Diesel?
