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Cars don’t have better mpg

By Tara Baukus Mello ·
Wednesday, January 11, 2012
Posted: 9 am ET

If you feel like your car today doesn't get any better gas mileage than cars you’ve owned previously, it probably isn’t in your imagination. A new MIT study shows that, while there have been major advances in fuel efficiency technology over the last few decades, there have been only minor improvements in actual fuel efficiency due to the increased weight and horsepower of today's cars.

The study, conducted by MIT economist Christopher Knittel and published in the American Economic Review, looked at the data between 1980 and 2006. During that span, the average fuel economy of autos sold in the U.S. increased by more than 15 percent, yet the average curb weight has increased 26 percent while horsepower went up 107 percent. As a result, if today's cars were the same weight and horsepower as they were in 1980, the fuel economy average would have jumped from the then average of 23 mpg to about 37 mpg, according to the report.

Today's cars average about 27 mpg, so Knittel points out that, "most of that technological progress has gone into compensating for weight and horsepower."

Tara Baukus Mello writes the cars blog as well as the weekly Driving for Dollars column, providing both practical financial advice for consumers as well as insight into the latest developments in the automotive world. Follow her on Facebook here or on Twitter @SheDrives.

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March 06, 2012 at 2:12 pm

Interesting. So the power:weight ratio has gone up 64% in that time (so it's 1.64x what it was).

And this really affects all classes of cars - there's not going to be anything on sale now, for example, that's as slow as the Rabbit Diesel. Or, I would expect, as slow as a guzzler equipped with the wheezy GM "Iron Duke" engine.

Yet people still won't buy eco-friendly models because they're seen as being - and I quote - "dangerously slow". Never mind that the most economical thing they could buy would probably still be measurably faster, particularly in real-world conditions rather than on-track, than a bog-standard one from the uncaring 80s.

I'm driving what would probably be classed as an eco-car now - and not only that it dates from 2003, not 2012, so it's tech and performance are still a little behind the times. It's the second fastest thing I've ever owned, and it doesn't have to be worked anywhere near as hard for the same day-to-day performance as the 1st or 3rd placers, as it's tuned to give good real-world speed despite being identifiably not a high-horsepower racer when you really stress it. But it gets 50% better mileage than either of those... (in fact, more than 50% - but when the difference in price of it's "alternative" fuel is considered, it's almost exactly that).

I figure if it were tossed into the American landscape, surrounded by vehicles with "acceptable" economy that works out to consuming twice the volume of fuel per mile, it'd be perfectly capable of holding it's own against the majority when paired with "normal" drivers (as opposed to, say, Vin Diesel (ironically)), and run rings around most of the rest.

It's all marketing. Marketing, and playing on people's fears. I would be perfectly happy to have a crash against a hummer in my little "blue rollerskate". The exterior shell is exquisitely designed to funnel the crash energy away from the passenger cabin, which on the inside turns into a five-seater bouncy castle -cum-rollercoaster thanks to the preponderance of airbags and the "smart" seatbelts. Or to run a red-light drag against joe average in his Dodge.

But if you listen to the advertisements, you'd think that going out in anything less than a Ram 6.0 Hemi would put you at risk of being overtaken by pedestrians, and dying a terrible bloody death if a leaf brushes your radiator grille.

Follow J-Lo instead. Despite the terrible commercial that she made, she (or at least, her character) knows the score.
(...and the less said about that particular car only being available in the states with the largest, most overpowered, least efficient engine in the entire range, the better...)

March 04, 2012 at 5:20 pm

I have an 06 plate 1.6 diesel with over 90K on the clock, my fuel consumption average is 64 mpg. Fuel consumption will depend directly on driving technique and car maintenance.

Colin Stone
February 26, 2012 at 9:03 am

The fuel economy of these so called 60mpg + cars is rubbish. My 12 year old VW Golf 1300kg has a manufacturer's combined economy of 57.6 mpg/CO2 132g/km and over 12 years has averaged 55mpg. Looking at all the new sub 100g/km cars with around a combined fuel economy of 74mpg, they actually average out at 54mpg when real ownership figures are used.

stormy petrol
February 03, 2012 at 6:39 pm

You guys are right on with the comments about increased weight meaning worsening fuel economy and performance. My favourite lighweights from back in the day are the very attractive Panhard CT24 (795 kg, half a current car's) and the first (alu-bodied) Lancia Fulvia Zagato. Had a regular Fulvia coupe which was just a great, great car. A crying shame that these makers have affectively ceased to exist, while the Toyotas of this world make hay...

January 29, 2012 at 4:20 pm

The top 30 European cars for economy in the UK and Europe, all capable of achieving 5 stars (the highest rating) in the NCAP safety tests which equals or exceeds all US safety tests...And with emission often below 100 gm/Km... Average 60 mpg (US) combined.

These are fast capable, comfortable cars.

America is currently enjoying the average fuel consumption for it's new cars that Europe had in the 1960's ...Well done!

The technology is there ...

Horatio Hornblatt
January 22, 2012 at 5:08 pm

Randy61, you're dead on. Yes, the engines are more efficient and powerful, but the "crashworthiness" mandated engineering made the autos weigh more. The answer: More high-tensile strength steel is now being used for stronger, lighter vehicles. The down of course, it's more expensive.

January 21, 2012 at 5:17 am

They didn't tell the rest of the story though. Before the 80's we didn't have mandated safety equipment that made the cars heavier nor did we have all the Government mandated emissions equipment that drained all the power out of them (which has taken years for automakers to figure out to regain). If the government had never interfered with any of this, we probably would have cars now that would be just as powerful AND get twice the MPG.