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More transportation articles by David LawyerCopyright 2008 by David S. Lawyer. Feel free to make copies but commercial use of it is prohibited. For example, you can't (except to an insignificant degree) combine it with advertising on the Internet. Please let me know of any errors or suggestions for improvement.
Passenger transportation in the U.S. is a major contributor to global warming and depletion of petroleum resources. Due to increasing oil consumption and decreasing oil production in the U.S., we now have to import almost 2/3 of our liquid fuel. Most of this fuel is used for transportation with about 2/3 for passengers and the remaining 1/3 for freight. The cost of importing oil is one cause of our burgeoning foreign debt which is growing at a rate of over a half trillion dollars a year and contributing to the current economic crisis in the U.S.
Our current passenger transportation system is auto-airplane based with less than 1% of travel (in passenger-miles) via rail (including rail transit), with about 15% of travel via air. Our travel consumes about 40 times as much fuel as it did in 1900 when almost all motorized travel was by railroad (including electric streetcars and light rail). Why did fuel consumption increase so much. Was railroad transportation in 1900 more energy efficient? No! It turns out that today our automobiles and airplanes are roughly 5 times more energy-efficient in terms of passenger miles per gallon (or the like based on the heat equivalent of various fuels). But before explaining why we are 5 times more efficient today, it's necessary to first explain how it's possible to consume 40 times more fuel when the efficiency goes up 5 times.
This higher fuel consumption is because of more travel and more people. In 1900, each person traveled by rail about 330 miles per year (on average) even though the steam railroad network was nearly 200,000 miles long plus 14,000 miles of electric light-rail/streetcar lines. Today, each person (on average) now travels about 50 times as many miles, mostly in automobiles, SUVs, and airplanes. Also, there are about 4 times as many people. So today there is almost 200 times more travel than in 1900. This more than cancels out the 5 times better efficiency and results in about 40 times more fuel being consumed (200/5 = 40).
How could rail have been so inefficient in 1900? It's due to: inefficiency of both steam locomotives and electric power generation as well as heavy trains. Passenger trains were (and still are) very heavy, weighing about 4 times as much per passenger as an auto. In 1900, they only got the equivalent of about 6 passenger-miles per gallon. For electric streetcars, it took about 8 times as much fuel in 1900 than it does today to generate a kilowatt-hour of electricity. Thus the 14,000 miles of streetcar lines in 1900 were not very energy-efficient either and got the equivalent of about 7.5 passenger-miles per gallon. Later on in the 20th century, with the introduction of diesel locomotive and more efficient electricity generation, trains rail became significantly more energy-efficient than the automobile.
An auto that gets only 20 miles/gallon will get 40 passenger-miles per gallon if it has two people in it (20 x 2 = 40) so "passenger-miles per gallon" for autos will always be larger than the "miles per gallon" values. The average number of people per auto is claimed to be a little under 1.6 while it's over 1.7 for a SUV. Based on the above, autos now get about 35 passenger-miles per gallon while SUVs get about 28 passenger-miles per gallon. Airplanes get about 38 passenger-miles per gallon which at first glance, seems to be better than the auto. But it's actually a little worse if one compares it to autos used on long trips. Such long trips usually have more people in the auto and also get better miles-per-gallon than in city driving.
What causes us to travel so much more today than we did over 100 years ago? It was mainly due to the automobile and the airplane (along with the roads and airports that support them). With the auto, one could go anywhere, anytime, and was not constrained to fixed rail routes and schedules. Then housing, stores, and workplaces, located themselves based on auto accessibility, making long trips via auto almost a necessity rather than an option. With air travel, the high speed meant that a passenger could consume many times more fuel per hour than they could in an automobile.
But it's overly simplistic to put the whole blame for greatly increased travel on just the auto and airplane. Don't forget that the railroads were also an enticement to travel. Even after the automobile appeared on the scene in 1900, rail travel nearly tripled, reaching its peak in 1920. Before railroads first appeared in the 1830's, travel was mostly by foot, animal power, and sails, all of which used solar energy. So it was first the railroad, then the automobile, and later on the airplane that enticed us into unsustainable amounts of travel. Each new type of travel resulted in huge increases in both the total amount of travel and fuel consumption.
When people bought their first auto in the 1920's and switched from public transportation to the more energy-efficient automobile, did this save any energy? The auto was then a few times more energy-efficient than steam powered trains and also more efficient than the streetcars and light rail. But energy consumption didn't decrease. During the 1920's, automobile travel increased 6 times, steam railroad travel decreased by about 40% and streetcar/light-rail travel decreased by about 20%. As a result, automobile travel increased roughly 15 times faster than the decrease in rail travel, resulting in much more energy being consumed, even though the auto was more energy-efficient at that time.
Ironically, the largest improvements in energy-efficiency during the 20th century were made by rail, which also lost almost all of its market share of passengers to autos and airplanes. Steam locomotives were phased out over a 20 year period, starting in the late 1930's, and replaced by diesel locomotives. This resulted in passenger railroads becoming roughly 50% more energy-efficient than the auto. More efficient electricity generation resulted in electric streetcars/light-rail becoming more efficient than the auto by about 1930. But unfortunately, it didn't make much difference, since auto travel had overtaken rail travel in the early 1920s and by 1930 there was about 6 times more travel by auto than by all types of rail.
Today, unfortunately, the energy-efficiency of rail travel is little better than that of the auto. It could be much better if trains were more efficiently designed and operated, including doing a lot of coasting to save energy. Urban bus energy-efficiency is also about the same as the auto.
It's interesting to speculate how much less energy we would use for travel if we had stuck to railroads and if the auto and airplane hadn't been invented. Without autos and airplanes, we would travel far less than we do today. Even if rail travel per person had increased several times from the 330 miles per year in 1900, this could have been compensated for by the increase in rail energy-efficiency. So we might still be using about the same amount of fuel per person we used in 1900 (40 times less than today). Unfortunately, the increase in population by almost 4 times would increase fuel consumption but we might still be using only about 10% of the fuel we use today for travel. Thus if rail was the only method of motorized travel today, we would use far less travel energy, not because of railroads but because of less travel.
When the energy crisis hit the U.S. in the 1970s and the U.S. government sponsored studies on transportation energy efficiency, mass transit and railroads were then roughly twice as energy-efficient as the gas-guzzling auto. As compared to airplanes, the auto was about twice as energy efficient and mass transit about 4 times better. Much of what one finds in print today (and on the Internet) is unfortunately based on these now obsolete studies from the 1970s. In addition, some elements of the mass transit industry published misleading claims of high transit energy efficiency by showing how efficient a hypothetical train could be that ran at steady speed on level ground and was otherwise very energy-efficient. But this isn't the typical train. All this tended to mislead many people into thinking that mass transit and railroads today are much more energy-efficient than they actually are.
Today, the auto is no longer the gas guzzler that it once was (except for some SUVs). Mass transit is in some cases less efficiently designed and operated and has more empty seats. Airplanes have significantly improved their energy-efficiency by less empty seats, flying at higher altitudes, and using larger fans in their engines (which are like hidden propellers). There is also unrealized potential for making rail and urban buses more energy-efficient but it hasn't happened yet.
So what lessons can be drawn from our brief glimpse into the history of travel fuel economy? One is that increasing energy-efficiency doesn't always save energy. This is not a new discovery as it was pointed out by Jevons in the 19th century in his book "The Coal Question". There are many other examples of this phenomena. Increasing energy-efficiency without restricting the growth of travel can often lead to more fuel consumption, not less. History indicates that the reason for our voracious appetite for fuel for travel is mainly due to too much travel per person as well as population growth. It also indicates that the main reasons we used much less energy when we were mostly dependent on public transportation and railroads was not because they were energy-efficient (they often were not), but because we traveled a lot less and there were fewer people.
Thus to reduce energy, the author believes that the main effort should be to reduce travel along with supporting negative population growth. There are also many opportunities today for increasing the efficiency of both automobile and rail/bus transportation. But if increasing efficiency leads to a corresponding growth in travel, the benefits of energy-efficiency may be undone.
For the sources of data and estimation methods for this article see: Fuel-Efficiency of Travel in the 20th Century