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New UMTRI report on US vehicle fuel economy from 1923-2013 suggests need to focus on improving lower tails in each vehicle class

In a new report, researchers at the University of Michigan Transportation Research Institute (UMTRI) have calculated the actual, on-road fuel economy for the entire fleet of all vehicles in the US, and for different classes of vehicles, with primary interest in light-duty vehicles (cars, pickup trucks, vans, and SUVs), between 1923 and 2013.

The main findings from the analysis are that fuel economy decreased from 14.0 mpg (16.8 l/100 km) in 1923 to 11.9 mpg (19.6 l/100 km) in 1973. Starting in 1974, fuel economy increased rapidly to 16.9 mpg (13.9 l/100 km) in 1991. Thereafter, improvements have been small, with fuel economy in 2013 at 17.6 mpg (13.4 mpg US). Overall, the results suggest, the authors conclude, that efforts on improving fuel economy should focus on the lower tails of the distributions of fuel economy in each vehicle class.

On-road fuel economy of vehicles from 1923 to 2013. Source: Sivak and Schoettle. Click to enlarge.

The new study by Dr. Michael Sivak and Brandon Schoettle updates a 2009 analysis of actual, on-road vehicle fuel economy in the United States from 1923 through 2006, extending the data through 2013, and including retroactive adjustments made to several values by the US Department of Transportation.

By category, they found:

  • All on-road vehicles. From 1923 through 1935, on-road fuel economy stayed approximately constant at around 14 mpg. Starting in 1936, fuel economy gradually declined, falling to its lowest level, 11.9 mpg, in 1973. In 1974, fuel economy began to increase rapidly to 16.9 mpg in 1991. Thereafter, improvements have been small.

  • Cars. On-road fuel economy decreased from 1936 to 1973, followed by major improvements from 1973 to 1991. Improvements since 1991 have been small, with fuel economy at 23.4 mpg in 2013.

  • All trucks. For all trucks combined, the on-road fuel economy decreased from 10.2 mpg (23 l/100 km) in 1936 to 7.8 mpg (30 l/100 km) in 1965.

  • Light trucks. On-road fuel economy of light trucks increased rapidly from 9.7 mpg (24 l/100 km) in 1966 to 17.0 mpg (13.8 l/100 km) in 1991. However, the improvements since 1991 have been small, with fuel economy at 17.2 mpg in 2013.

  • Medium- and heavy-duty trucks. Since 1966, on-road fuel economy of medium- and heavy-duty trucks has improved from 5.6 mpg (42 l/100 km) to 6.4 mpg (36.7 l/100 km) in 2013.

Broadly, although fuel economy decreased from 1935 to 1973, this does not imply that powertrains for vehicles did not improve during this period, Sivak and Schoettle noted. Engineers were focused on increasing power and acceleration rather than fuel-economy improvements.

As has been argued eloquently by Larrick and Soll, equal absolute increases in miles per gallon result in greater fuel savings as the initial fuel economy of a vehicle decreases (despite what most of us intuitively believe).… This observation, however, does not necessarily argue that we should focus our efforts on those classes of vehicles that currently have the lowest fuel economy, such as medium- and heavy-duty trucks, and buses. For medium- and heavy-duty trucks, the relevant societal measure is not miles per gallon but ton-miles of freight per gallon. Alternatively, the relevant measure for buses is passenger-miles per gallon.

The above observations suggest that our focus should be on the lower tails of the distributions of fuel economy in each vehicle class. In other words, society has much more to gain from improving a car from 15 mpg to 16 mpg than from improving a car from 40 mpg to 41 mpg. Similarly, the benefits to society are greater from improving a truck from 4 mpg to 4.5 mpg than from improving a truck from 7 mpg to 7.5 mpg (while keeping the load-carrying capacity the same).

—Sivak and Schoettle




The best way to improve the fuel economy of US vehicles would be to add say $1 / Gallon in tax.
Currently they are using a mandated "push" approach with CAFE, etc, but if you coupled that with a "pull" from fuel prices, you would really get things going.
It is a good time to do it: oil prices are very low and cars are more efficient than they have ever been. Even 5 year old cars are reasonably good so people with less cash can afford them.
$1 might be a bit of a mouthful, but if you did $0.20 / year for 5 years, you would get the same effect with less shock.
As everyone knows, we have fuel prices more than double US values in Europe and everyone gets by, so it wouldn't be the end of civilization or anything like that. People would just drift across to cars with smaller engines, diesels or hybrids.

A question is: should you go for a $1 "big bang" tax increase or 5x $0.20 smaller jolts.
A big bang will have an immediate, dramatic effect, and once it is done, it is done.
A set of smaller ones will cause less short term hardship, but have less "shock and awe", and could be cancelled by the next president.
You could spend the extra taxes only on transport - there is lots of infrastructure that needs to be maintained, and a bit on rail / public transport as well.


I think that a policy promoting a consistent annual increase in the gas tax is required. The revenues should be split between tax reductions for the lower income groups and spending for infrastructure and social security. The most important thing is to have a dependable increase in fuel costs. If for political reasons it needs to be mostly revenue neutral then so be it.


Increase the U.S. federal gas tax to 25 cents per gallon, then make it a percentage of gasoline price. California SB350 would decrease fuel usage 50% by 2030.


So you want to raise the price of energy to curb its use?
Okay, who hurts more, lower income people or people with wealth?

Its not a vice to most people to drive their car to work, why tax it like one?

Until there are viable alternatives for most Americans this course of action shouldn't be on the table.

Gas doesn't play well with supply and demand. Demand is inflexible, people will pay for it until they can't. Why create a new class of welfare, entitlement, bureaucracy and oversight?

What is the end to the means of raising the gas tax?

Why not push for more "green" fuels? EVs and waste to fuel... or any other alternatives?

What if gasoline was made from waste? would we need such a tax?

or is this just a way to subsidize EVs?

thomas p

The key is getting manufacturers to introduce Euro style diesels. Cars in Europe get 60 mpg while the best US mpg is around 40.


I'd never go for a small diesel over a gasoline ice anytime soon. Its one thing for a work truck and a different thing for a passenger car... Tier 4 emission equipment needs a drive cycle with heavy loads. Everything about modern diesels are extremely expensive. Injectors, high pressure pump, fuel rail pressure sensors, nox. Catalyst, DPFs, nox sensors, ECT.

There is so much overhead on a diesel, and its so sensitive to user operation I can see why any manufacturer would be scared to bring one over. That and people cannot figure out the difference between DEF and diesel.

Diesel has to overcome a huge price difference, and the payback wont be for a long while.

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