October 04, 2007
Fuel Efficiency Decline Reverses In United States

The long term trend toward lower fuel efficiency cars in the United States appears to have stopped and slightly reversed in the face of more expensive gasoline and diesel fuel.

Compared with 1987, the average weight of the vehicle we drive has risen by 923 pounds, or 29%. The average time it takes for a vehicle to go from zero to 60 miles per hour time has dropped to 9.6 seconds -- the fastest since the EPA started compiling this data in 1975. Our average car or truck has 223 horsepower, and the most horsepower per pound on record.

There is some good news: The 17-year decline in the average fuel efficiency of America's new car fleet that began in 1987 appears to have stopped. The EPA forecasts that the average fuel economy of 2007 model cars and trucks will be 20.2 miles per gallon, the same as 2006 and slightly better than 19.9 mpg measured for 2005. That would make three straight years when the new vehicle fleet's fuel economy was no worse, or slightly better, than it was in 2004.

The writer is getting this information from a new US Environmental Protection Agency report Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2007.

The rise in vehicle weights and decline in fuel efficiency were mostly the result of rising affluence. If inflation adjusted fuel prices stay the same (and fuel prices both declined and rose during the study period) rising incomes will enable people to spend more on fuel. It takes declining living standards or large rises in fuel prices to change consumer demand. Taxes and regulations on gas guzzlers can force people toward more fuel efficient vehicles even if gasoline and diesel stay relatively cheap.

Of course, oil prices have quadrupled in the last 8 years and my guess is they are going to go much higher.

So should we be worried or angry that fuel efficiency of US cars and trucks got worse for so many years? Is the poor fuel efficiency of 4000 lb cars reason to expect US society to collapse once world oil production starts declining a few percent per year and oil exports start declining 5 per cent per year? Is doom and gloom straight ahead?

My take: Our profligate use of energy is a reason for optimism. That the average light duty vehicle sold in the US in 2007 weighed 4144 lb (up from 3221 lb in 1987 in spite of materials advances) means that we could greatly increase fuel efficiency by riding around in 2600 lb vehicles and still live fairly comfortably and drive quite a lot. That car acceleration from 0 to 60 mph increased from 14.4 seconds in 1975 to 9.6 seconds in 2007 means we could go back to 1975 rates of acceleration and gain even more fuel efficiency. Plus, we could switch to diesel hybrids and gain even more fuel efficiency. We could do all this before embracing pluggable hybrid electric vehicles. So it seems we could adjust to a halving of our current rate of oil consumption and still live pretty well.

A lot of people who forecast Peak Oil hitting either starting a couple of years ago or Real Soon Now will give you a very doomster view of the future. But especially for the countries that have the highest living standards there are huge margins for adjustment. Living standards will take a hit while we migrate to an electric economy and spend on efficiency enhancing technologies. But we have lots of suitable technology to help make the adjustments and more technological advances in the pipeline.

Share |      Randall Parker, 2007 October 04 07:24 PM  Energy Transportation

Rob said at October 5, 2007 9:00 AM:

Hi Randall,

There's a book out now called Zoom about the possible future of cars and fuel efficiency/oil indepedence. You might want to review it, or just read it.


Barry Parki said at October 5, 2007 5:23 PM:

One of the major factors that is regularly overlooked regarding the increasing weight and price of cars is safety and pollution improvements. The bumpers are stronger and heavier. The sides are now constructed to resist impact. Extra space behind the engine and frame design now causes a front end impact to push the engine down and create more crumple room while protecting the passenger compartment. Roll over safety is improved. Safer seats, multiple airbags front & side. All these add weight. The gas tank is larger to allow expansion room to avoid overflowing on hot days and is shielded to prevent fire into the passenger compartment in event of collision.

This extra weight comes even with many alloy parts and hi output engines and drive trains that weigh much less than comparable parts & engines only 10 years past.

This problem is dynamic, in that increasing mass then requires an increase in size of other components to handle the increased weight. A 5 lb additional feature may result in another 1/2 lb weight increase in the system to accomodate that increased mass.

It is not only the increasing size and performance we are paying for but pollution and safety features. Improvements have unintended consequences too.


Doug Dante said at October 5, 2007 9:59 PM:

"we could go back to 1975 rates of acceleration and gain even more fuel efficiency"

Regulating acceleration won't work. Acceleration is one feature of a substantial engine. Towing capacity is another. Many people either need to tow big trailers and boats with their big SUVs and trucks, or they like the idea that they can do so.

If you regulate acceleration, auto companies will just change the software on those big trucks to accelerate more slowly, and you'll create a huge aftermarket for software that isn't crippled. It will provide some fuel efficiency benefits, but not what you expected.

If the goal is to reduce fuel consumption, then increasing fuel cost is the best and most effective way to do this - as we have seen. :(

Randall Parker said at October 5, 2007 10:13 PM:


If the Peak Oilers are correct those higher prices are on the way.

Engineer-Poet said at October 6, 2007 5:37 PM:

We should have imposed those higher prices ourselves, via taxes.  This would have kept demand lower and left billions of dollars in the US economy every year instead of sending it to oil exporters (many of which are our ideological enemies); the US imports roughly 5 billion barrels of oil per year, and if our measures cut that figure by 10% and reduced the world price from today's ~$80/bbl to $70 we'd save $85 billion.  That's about $280 for every American.

Tom said at October 9, 2007 6:25 AM:


"One of the major factors that is regularly overlooked regarding the increasing weight and price of cars is safety and pollution improvements. The bumpers are stronger and heavier . . ."

Actually, bumpers are generally weaker. There used to be a 5 MPH requirement for bumpers. That was reduced to 2.5 in 1983. Consequently, low speed collisions generally cause more damage than they used to. But you're probably right on the rest - in terms of overall safety, we're better off now.

Brett Bellmore said at October 11, 2007 4:02 PM:

I continue to be convinced that eventually bumpers will be replaced with external airbags, triggered in advance of collisions by sensors monitoring the environment around the vehicle, and extrapolating trajectories. It's really the only solution for crash resistance which is compatible with high mileage, and which protects not just the occupants of the car, but anybody hit by the car, too.

But then, I've been convinced of this for at least a decade, and they haven't shown up at the dealer yet. What gives?

Engineer-Poet said at October 13, 2007 9:10 PM:

Cost, reliability and liability, in reverse order.  If you think the lawsuits over injuries from airbags inside cars are bad, just think about the possibilities of lawsuits from injuries to bystanders from external airbags.

The way to fix that problem is to make the vehicle lighter without cutting the size (and streamline it).  Lighter, fluffier vehicles will absorb energy better.

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