Vehicle Weight Vs. Fuel Economy Study Ignores Gov Mandates

Illustration for article titled Vehicle Weight Vs. Fuel Economy Study Ignores Gov Mandates

A new non-profit study, "Automobiles on Steroids: Product Attribute Trade-Offs and Technological Progress in the Automobile Sector," criticizes all automakers over lower fuel economy due to higher power and vehicular weight gains since 1980. It's a complete load of crap.

The paper, written by Christopher R. Knittel and registered with the National Bureau of Economic Research (NBER), posits the following in it's abstract:

New car fleet fuel economy, weight and engine power have changed drastically since 1980. These changes represent both movements along and shifts in the "fuel economy/weight/engine power production possibilities frontier". This paper estimates the technological progress that has occurred since 1980 and the trade-offs that manufacturers and consumers face when choosing between fuel economy, weight and engine power characteristics. The results suggest that if weight, horsepower and torque were held at their 1980 levels, fuel economy for both passenger cars and light trucks could have increased by nearly 50 percent from 1980 to 2006; this is in stark contrast to the 15 percent by which fuel economy actually increased. I also find that once technological progress is considered, meeting the CAFE standards adopted in 2007 will require halting the observed increases in weight and engine power characteristics, but little more; in contrast, the standards recently announced by the new administration, while certainly attainable, require non-trivial "downsizing". I also investigate the relative efficiencies of manufacturers. I find that US manufacturers tend to be above the median in terms of their passenger vehicle fuel efficiency conditional on weight and engine power, and are among the top for light duty trucks; Honda is the most efficient manufacturer for both passenger cars, while Volvo is the most efficient manufacturer of light duty trucks. However, I also find that over time, US manufacturers' relative efficiency in both passenger cars and light trucks has degraded. These results may provide insight into their current financial troubles.


First we'd just like to say as consumers of horsepower and torque, we're quite happy with the improvements since 1980. We're wondering if Mr. Kittle has ever tried to merge into freeway traffic in a 1980 Toyota Corolla. Not a pretty sight.

In any case, the content of the study would be far more interesting to us if it didn't seem from the outset the author was only interested in painting automakers as wasteful and the automobile and its consumer the same way. We say this because despite mentioning technological advancement since 1980, there is absolutely no mention of the government mandates in improvement to emissions and safety. We can understand a statistical analysis of fuel economy versus weight and power, but to completely ignore mandates which add considerable girth to a vehicle is a major oversight which seems intentional.

Sure, cars are much bigger and more powerful than they were in 1980, but they also always start in the morning, aren't actively trying to kill you in a crash and don't spew blue smoke anymore. The inclusion of primary, secondary and now tertiary airbags alone adds weight and cost, not to mention ever increasing structural requirements in both the safety cage and crumple zones. We're not saying we don't like the idea of the study, as more information put into context is always better, but when you leave out an obvious weight driver the whole affair is suspect. (Thanks for the tip Andrew)


Photo credit Think Or Thwim, sculpture by Irwin Wurm

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Ash78, voting early and often

Completely ignores safety and comfort (weight gains), which are probably a bigger driver of engine power than consumers simply screaming "moar powah!"

However, for a long time I've been wondering what would have happened if engineers spent more time on efficiency before power. Honda can squeeze 255hp(?) out of the Accord V6 and still give it high-20s on the highway. But could they also have managed 35mpg on 200hp? Probably not, but it's worth considering those tradeoffs.

My back-of-envelope crunching shows a lot of examples where power can be increased substantially with a very small hit in economy, so that power/efficiency frontier isn't exactly linear. It favors power. #fueleconomy