BLUFF: Improved fuel efficiency is good, all other things being equal. All other things are never equal.
On the subject of fuel efficiency, let’s arbitrarily confine ourselves to three areas.
1. User fuel consumption and emissions
2. Manufacturing fuel consumption and emissions
3. Whole life fuel consumption and emissions
You can do this a million different ways, but these are convenient.
1 is what I was talking about in the previous post, and it’s what most manufacturers advertise. It’s less significant than it appears. The ur-example is fuel consumption for a hybrid vs a pure ICE vehicle. The hybrid may get better gas mileage for the owner, but various parts need to be shipped, batteries produced, other components manufactured, etc. The hybrid may have better (lower) user fuel consumption/emissions (1) but worse (higher) manufacturing fuel consumption/emissions (2). In situations wherein much of the user level emissions are not controlled by the user, ie the power-generation mix of the power company, the advantages from an emissions perspective can be very complicated.
1 is fairly easy to measure.
2 is hard to measure and often kept secret.
3 suffers all of the problems of 2.
We can model 2 with the purchase price, but that’s not a great model.
From an environmental perspective, we want to minimize 3. From a personal financial perspective, we want to minimize (1 + cost of purchase). The government tends to increase costs on 1 to reduce total emissions, regulate 2, and completely ignore 3.
The point here isn’t that improved fuel efficiency is bad. It’s that one should be careful to be sure what one is evaluating is indeed what one thinks it is. See the tag line.