Ford of Europe to increase EcoBoost engine production by 35% form 2013-2015
16 more US employers and 2 stakeholder groups join DOE Workplace Charging Challenge

Study finds that increased vehicle travel and decreased occupancy have undercut the impact of improving fuel economy over last 40 years

A new study by Dr. Michael Sivak, Director, Sustainable Worldwide Transportation, University of Michigan Transportation Research Institute (UMTRI), has found that from 1970-2010, an increase in vehicle distance travelled in the US, coupled with a decrease in the number of occupants in the vehicles, combined to undercut the impact of advances in vehicle fuel economy during that period.

From 1970 to 2010, vehicle distance travelled in the US increased by 155% (from 1.674 trillion km to 4.260 trillion km); however, because vehicle load (i.e., occupants carried) decreased by 27% (from 1.9 to 1.38 persons), the occupant distance travelled increased by 84% (from 3.182 to 5.867 trillion km). Sivak found that while the vehicle fuel economy of the entire light-duty fleet improved by 40% (from 13 mpg US to 21.6 mpg US, or from 18.1 l/100km to 10.9 l/100km), because of the decrease in vehicle load, the occupant fuel economy only improved by 17% (from 24.8 mpg US to 29.8 mpg US, or 9.5 to 7.9 l/100km).

As a consequence of the changes in vehicle fuel economy, vehicle distance travelled, and vehicle load, the total amount of fuel used increased by 53% (from 303 to 463 billion liters).

—Sivak 2013

According to the 2011 American Community Survey by the US Census Bureau, 79.9% of workers not working at home drove to work alone.

The study includes a brief discussion on the effects of potential future changes in vehicle fuel economy, vehicle distance travelled, and vehicle load on the amount of fuel used for personal transportation.

Sivak notes that:

  • Nominal reductions in fuel consumption due to improved fuel economy need to be adjusted downward due to the rebound effect. (EPA recommends a 10% decrement.) In other words, a 20% increase in fuel economy would result in a net 18% reduction in fuel consumption.

    Because changes in fuel economy take a long time to percolate through the entire fleet, an 18% reduction in fuel used by vehicles purchased in a given year (due to a 20% improvement in their fuel economy) would result in only about a 1% reduction of the fuel used by the entire fleet.

    (This has led some researchers to argue that the policy emphasis should be on reducing vehicle distance traveled through an increased fuel tax—with fleet-wide effect.)

  • Because the amount of fuel consumed is directly proportional to vehicle distance traveled (holding everything else constant), a 20% decrease in vehicle distance traveled would translate into a 20% reduction in fuel used.

  • Increasing occupancy (e.g., through ride sharing) reduces vehicle distance traveled, and also slightly worsens fuel economy due to the extra weight. In a scenario of increasing vehicle load by 20% from the current 1.38 to 1.66 occupants, vehicle distance travelled would be reduced by about 15%, while vehicle fuel economy would worsen by about 1%. Combining these two effects yields a reduction of about 14% in the amount of fuel used.

The study was supported by Sustainable Worldwide Transportation. The current members include Autoliv Electronics, Bridgestone Americas Tire Operations, China FAW Group, General Motors, Honda R&D Americas, Meritor WABCO, Michelin Americas Research, Nissan Technical Center North America, Renault, Saudi Aramco, Toyota Motor Engineering and Manufacturing North America, and Volkswagen Group of North America.


  • Michael Sivak (2013) Effects Of Vehicle Fuel Economy, Distance Travelled, And Vehicle Load On The Amount Of Fuel Used For Personal Transportation In The US: 1970-2010 (UMTRI-2013-10)



"As a consequence of the changes in vehicle fuel economy, vehicle distance travelled, and vehicle load, the total amount of fuel used increased by 53% (from 303 to 463 billion liters)."
But keep in mind that the US population increased by a similar percentage (52%)during the 1970-2010 period (see US census data). If average driving distances have indeed increased and user occupancy decreased, those factors have actually probably been totally made up for by increases in efficiency. What remains is more fuel being used to move around many more people.


I think this confirms that no matter what the price of fuel or the efficiency of the vehicles the consumer mentality of the US populace will always drive them to consume to the highest level possible without consideration of the consequences. They will whine too. However, they could simply live within their means and save money rather than spend it. However, their lives are empty shells of superficiality and they must fill the void with useless junk that no one needs. Our leaders are lucky too, that they have such a shallow, ignorant and easily manipulated mass of people out there. Otherwise they might actually be capable of improving the country and possibly they would be held accountable for their ineptitude rather than simply blaming the problems on the rank and file federal workers.


Yes, and 2012 will soon be officially declared (with 2011) the year with all time highest human made emissions.

Tokyo's goals may not be met for years/decades to come unless:

1. transition to electrified vehicles is accelerated.

2. dirty coal fired power plants are modified or turn down.

3. transition to clean e-power sources is accelerated.

4. Garbage dumps are eliminated or gas emission fully captured.

5. shale gas and shale/tar sands operations are cleaned up.

6. 101 other actions

It is fair to conclude that it will not happen this year or during this decade.


Interetingly, given the numbers presented here and the census data for 1970 and 2010, in forty years the per capita fuel usage rate in the US stayed at about 1,500 Liters. Wow-talk about stasis!


Adjusted for inflation, we are paying about the same for gasoline. People complain about $4 gasoline in the U.S., a gasoline tax would bring about a call to "throw the bums out".

The U.S. burns 300 million gallons of gasoline per DAY! I hope that number sinks in so people can really look at their consumption patterns and help reduce the amount of imported oil soon.


40 years ago most families only had one car and it was likely that only one parent had a job. Or at least that's how I remember my family.


After all that Reaganomic trickle down, 5% of the people ended up with 95% of the wealth increase.


So, essentially, we are each doing 50% more work, while using the same amount of resources. That's not all bad.

What I want to know is: what is the overall trend?

The article tells us that we are at the same level (per-capita) as in 1970, but what about 1980, 1990, 2000?

Have we passed "peak consumption", or did consumption bottom-out 20 years ago and it is now increasing?

Without more data, the fact that 1970 matches 2010 tells us nothing.


Imagine all the one car families not commuting great distances with twice the mileage compared to 1970, we might not be importing as much oil.

Kit P

"After all that Reaganomic trickle down.. "

I wonder if SJC was even born when Reagan was POTUS or is just a victim of a bankrupt California school system.

People do not drive great distances to work because they enjoy freeway driving. They want to their kids to go to schools controlled by teachers dedicated to educating children not a bunch of draft dodging hippies who are as stoned as the gangs that have took over the schools.



Those kind of comments don't help the discussion.


I like the advanced concepts and higher math presented.

"Because the amount of fuel consumed is directly proportional to vehicle distance traveled (holding everything else constant), a 20% decrease in vehicle distance traveled would translate into a 20% reduction in fuel used."

Oh, and the discussion is beyond help.


In 1982 we had high inflation, then Reagan signed a bill taking away interest deductions for credit cards and car loans, arguably the largest tax increase on the middle class ever.

Now you have BOTH adults in the household having to work and needing two cars to commute to and from work. Even though fuel mileage was up, so were the number of cars and miles driven.

I was pointing out some of the driving forces that led to this, it was part of Reaganomics where the rich get richer and they did. Then we get comments about hippies and school systems.


What's wrong with the American school system? The lack of good science.

A few decades ago the fundies realised they had no hope of taking over in the national political stage so they focused on the small local systems - like the school boards. These are people who hate science. As it is now roughly half of the people in the United States reject one or more fundamental tenets of science (most commonly evolution), while a larger percent, perhaps more than 80 percent depending on how we measure, would fail a basic science test. A strong majority of those American citizens who would claim to have strong feelings about one or more science policy issues such as climate change, stem cell research, or nuclear power either know very little about the relevant science or are so badly informed regarding the science that their knowledge is not merely insufficient, but is actually opposite what is generally accepted by experts in the area. But then "somebody has to stand up to the experts"


Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)