I'm seeing some conspiracy theories making the rounds which claim that car-manufacturers are intentionally making cars that aren't as fuel efficient as they used to be. They often point to the Geo Metro and claim it got 50 mpg, which is better than even the modern hybrids.
Were cars like the Geo Metro really more fuel efficient than modern cars in the same class, and if so why?
There are a few things at work here:
Safety requirements and standards are much more strict now than they were 10, 15, or 20 years ago. These added components (such as ABS, etc) along with modern luxuries (such as power steering, etc) have added a lot of weight to modern cars. The Geo Metro you reference had a curb weight of just 820kg (about 1800 lbs), while the Yaris has a curb weight of 2311 lbs. That's a difference of 28.3%!
The EPA changed the standard way to estimate fuel economy in 2008. Here is a summary. The standards are now more strict, so I believe every estimate dropped when these went into effect.
Perhaps the fuel economy in general has gone down to make room for better performance as well, but I think that impact is minimal compared to the 2 items above.
Just for fun here is a link suggesting the opposite. They managed to average 48.5 MPG with the 2011 V6 Ford Mustang (this was not an EPA rating, but a test track rating, of course).
There are always outliers, but there is a standard in place for the US called CAFE (and a stricter standard in Europe) which requires the Corporate Average Fleet Economy to meet a minimum. Passenger cars are in a single category, and the standard for 2011 is 30mpg. 1995 was 27. There is a fine which manufacturers must pay if their fleet average falls below this requirement.
see: http://www.nhtsa.gov/cars/rules/cafe/FuelEconUpdates/2003/index.htm
Another possibile explanation for the perception (not for any statistics on performance) is a general shift in the way people drive. "Hypermilers" intentionally drive in ways that are proven to improve fuel efficiency. (Going slower, planning ahead to use the brakes less, etc)
I don't have any evidence to support this, but my own subjective observation is that in general there seem to be a higher percentage of aggressive drivers today than there were ten years ago. There is a lot of evidence[PDF-FuelEconomy.gov] to support the idea that agressive driving has negative effects on fuel efficiency. "Hypomilers"?
At higher speeds, typical of urban expressway driving, however, the fuel economy penalty of aggressive driving is both significant in magnitude and more consistent across all cars. The average car is likely to experience a penalty of 33 percent, with more powerful cars experiencing a somewhat lower penalty of about 28 percent. Hence the impact of agressive driving seems to be especially large at high speeds.
