This Appendix to "Fuel-Efficiency of Travel in the 20th Century" by David S. Lawyer, is about 5 times longer than the text part of this article. It's on the Internet and thus need not be printed with the article.
Some abbreviations are: PM = Passenger-Mile = pass-mi. For example BTU/PM is BTU/Passenger-Mile. gal = gallon. k = 1000.
April 2004: Added subsection on buses
March 2004: Used more recent data for Amtrak (for 2000 and 2001) showing a sharp drop in fuel efficiency.
August 2003: I discovered that the government "statistics" for air had apparently erroneously counted fuel used for air freight as being used for passenger transport. Mea Culpa for not being more vigilant. Of course the BTU/PM of TEDB for auto is "too low" for 1970-1989, and not "too high" as I erroneously typed in 2002.
July 2003: Originally (in June 2002) I estimated that the energy-efficiency in 2000 was 4 times that of 1900. It turns out to be over 5 times. The July 2003 version fixed that error. In 2002, I had both overestimated energy-efficiency for 1900 and underestimated it for 2000. For 1900, I failed to realize that old coal likely had a higher energy content (better quality) than today's new coal and erroneously used the data for new coal. It's still not clear exactly what the BTU/pound was for coal in 1900, so there could be future corrections. Since I didn't have the data for 2000 (in my 2002 version) I failed to take into account improvements in energy-efficiency so I used a low estimate of 30 pmpg for 2000 when it should have been 33 pmpg. See . I was just too hasty in making estimates and didn't refine them until July 2003.
[Ayres]: Energy Sources -- The Wealth of the World, by Eugene Ayres and Charles Scarlott, McGraw-Hill, NY, 1952. On p. 139, Fig. 1, is a graph of power plant fuel rates (energy-intensity) between 1902 and 1950.
[BusFacts-1935]: Bus Facts. 1935. p.9: chart: "Passenger-miles in United States by Various Means of Transport" (1890-1935). The chart is by H. E. Hale & Co., consulting engineers, 32 Nassau St., N.Y. There appears to be some double counting in this chart since the passenger-miles shown for Pullman Cars were also reported by the ICC for the Steam Railroads as shown in [ICC-Graph]. See also Bus Facts, 1966 (34th. edition) p. 6 "Intercity Travel in the United States 1929-1965". Bus Facts was published by NAMBO = National Association of Motor Bus Operators.
[BusFacts-1948]: Same as above but for 1948
[Bukovsky]: U.S. Interstate Commerce Commission, Bureau of Transport Economics and Statistics: Use and Cost of Railway Fuel and Problems in Fuel Statistics, Statement 4428 by Alexis P. Bukovsky (mimeographed 1944). At the University of Michigan Library.
[Census-1912]: U.S. Department of Commerce and Labor, U.S. Bureau of the Census: Central Electric Light and Power Stations and Street and Electric Railways, 1912. Washington: Government Printing Office (GPO) 1915 (series title of: "Special Reports"). This includes data for 1902, 1907 and 1912 and represents a merger of the two special census reports: 1. Central Electric Light and Power Stations. 2. Street and Electric Railways. They were issued separately in 1905 (1902 data) and 1910 (1907 data) but merged in 1915 with 1912 data included.
Not all the information from the 1905 and 1910 editions made it into the merged volume in 1915. For some 1902 data see also "Abstract of the Twelfth Census of the U.S." pp. 385+, 405+. U.S. GPO 1904. For some 1902-1917 (and 1918) data see: "Proceedings of the Federal Electric Railways Commission" U.S. GPO 1920, vol. 3 pp. 2222, 2229, etc.
[Energy in Am. Economy]: Energy in the American Economy, 1850-1975 by Sam H. Schurr and Bruce C. Netschert. The Johns Hopkins Press, Baltimore MD, 1960.
[Hilton]: The Electric Interurban Railways in America, by George W. Hilton; Stanford University Press, 1960. p. 186 shows line mileage from 1889-1959.
[Hirst]: Energy Intensiveness of Passenger and Freight Transport Modes 1950-1970 by Eric Hirst. Oak Ridge National Laboratory (then part of the U.S. Atomic Energy Commission, now part of the U.S Dept. of Energy), 1973 (ORNL-NSF-EP-44). This 39 page report is on the same topic as this article. With a limited scope of only a 20 year snapshot within the 20th century, it utterly failed to pick up the long term trend of increasing energy efficiency. In fact, per Fig. 3 (p. 21) it looks like all energy efficiencies are declining except for railroads.
[ICC-Graph]: Graphical Supplement to Monthly Reports, Series 1937 no. 4. Interstate Commerce Commission (ICC), 1937. Chart: "Steam Railway Traffic in Relation to Population, Years 1890-1936". See also "Passenger Transport in the United States 1920-1950" by Lewis C. Sorrell and Harry A. Wheeler. Railway Business Association, Chicago, 1944. p.3 Table No. 1 -Steam Railway Revenue Passenger Traffic of the United States, 1900-1940.
[Stat. Abstract 1930]: Statistical Abstract of the United States, (U.S. GPO) 1930, p. 423, Table No. 459: "Electric Railways". This has data for 1907-1927 (in 5 yr. increments). But footnote 4 indicates a serious problem with kwh figures prior to 1927).
[Chomitz]: "A Survey and Analysis of Energy Intensity Estimates for Urban Transportation Modes" by Kenneth M. Chomitz (Institute of Transportation Studies, University of California, Irvine, California 92717, December 1978.
[TransitFacts]: "Transit Fact Book" 1943- (annual) but has data back to 1920. By the American Transit Association (ATA). Starting with the 1974-75 edition, it was by the American Public Transit Association (new author). In 2002 it was "Public Transportation Fact Book" by the American Public Transportation Association (new name).
[TEDB]: Transportation Energy Data Book (annual) by Stacy Davis, Oak Ridge National Laboratory, U.S. Dept. of Energy. The most significant table is: "Energy Intensities of ... Passenger Modes" in Ch. 2. The latest edition is on the Internet. Ch. 2 is at Transportation Energy Data Book, Ch. 2. Edition 1 in 1976 was titled "Transportation Energy Conservation Data Book". Ed. 1.5 was issued in 1977. After 1981 (Ed. 5), the title word "Conservation" was dropped.
National Transportation Statistics by the Bureau of Transportation Statistics, U.S Dept. of Transportation. For 2003, see Table 4-20: Energy Intensity of Passenger Modes Amtrak energy is grossly low here since the energy in electric power is set equal to the fuel that would be used to generate the electricity if power plants were 100% efficient and there were no transmission losses. In reality, electricity generation (including transmission losses) is only about 30% efficient.
[Trans in Am.]: "Transportation in America" (annual) by the Eno Transportation Foundation, Washington DC. (Formerly Transportation Facts and Trends, by the Transportation Association of America) Some of their "statistics" are now found in the "Statistical Abstract of the U.S."). The 18th edition of Trans. in America is available with a "Historical Compendium 1939-1999" which covers years that other editions ignore. The table "Domestic Intercity Passenger-Miles by Mode" shows the modal split for intercity travel (but excludes international air travel).
[UrbanTransAndEnergy] "Urban Transportation and Energy: The Potential Savings of Different Modes", Congress of the United States, Congressional Budget Office. Washington DC, U.S. GPO, Dec. 1977. This uses data from other older reports, so it uses the poor fuel efficiency autos before federal mandates made them improve. It presents low, medium, and high estimates which often differ by a factor of 3. That's very confusing. But the Appendix contains much useful information.
Energy Efficiency and Sustainable Consumption, The Rebound Effect; edited by Horace Herring and Steve Sorrell, Palgrave Macmillan, 2008
This article's title, "Fuel-Efficiency ...", could also be called "Energy-Efficiency ..." since most all of the energy for passenger travel comes from fuel. Fuel-efficiency expresses efficiency in units such as passenger-miles per gallon of fuel. However, energy-efficiency would use units such as passenger-miles per million BTU, where BTU (British Thermal Unit) is a measure of heat content. Since there are about 125,000 BTU in a gallon of gasoline, knowing fuel-efficiency allows the immediate calculation of energy-efficiency and conversely.
Energy-intensity is just the inverse of energy-efficiency. Energy-intensity of travel for the United States is often expressed in units of BTU per passenger-mile. To get energy-intensity from energy-efficiency just divide 1 by the energy-intensity.
Thus the 3 different names: fuel-efficiency, energy-efficiency, and energy-intensity are basically the same concept (provide the same information), but are expressed in different ways. Outside of the United States, "kilometers" will be often used instead of "miles", heat values are more likely to be in kilo-calories (kcal) or mega-Joules (MJ) instead of BTU, and fuel volumes in liters instead of gallons.
See: Elements of Railroad Engineering by William G. Raymond, et. al. John Wiley, New York, 1923. p.157: Based on tests in 1904, simple freight locomotives consumed from 3.5 to 5 pounds of coal per horse-power hour. 4 lbs/hp-hr is only an efficiency of about 5% assuming a heat content of coal of 13.1k BTU/lb (U.S. Bureau of Mines). Internal combustion engines have an efficiency of about 25%. Both efficiencies are at steady speed and full power. Under actual operating conditions, the actual efficiencies will be significantly less.
On p. 251 of the 6th edition of Elements ... (1947) Raymond states: "The efficiency of the steam locomotive is only 7 per cent". This may have meant the efficiency of the latest models so the fleet efficiency may have reached a peak of about 6%.
See also Locomotive Performance by Wm. F. M. Goss. John Wiley, New York, 1907. See p. 101: For a locomotive built by the Schenectady Locomotive Works in 1891, fuel consumption was between 4.46 to 7.78 lb-coal per hp-hr. This is an efficiency between 2.52% and 4.39%. See also d"Comparative Tests of Run-of-Mine and Briquetted Coal on Locomotives" by Wm. F. M. Goss , U.S. Bureau of Mines Bulletin 37, 1911. It found thermal efficiencies with coal to be 3%-4% at the Pennsylvania Railroad test plants at Altoona, PA.
The approximate 6-fold increase in pass-mi/gal (equivalent) when railroads converted to diesel, tends to support these results.
The heat rate is the amount fuel used to generate a kilowatt-hour (kwh) of electricity. It's often given in units of BTU/kwh. But in olden days (before 1920) when coal was the principle fuel used, it was often given in units of lb-coal/kwh. For 1900, I've used the estimate of 6.0 lb-coal/kwh. This includes consideration of hydro-electric power so the figure for fossil-fuel generation would be higher at perhaps 7.25 lb-coal/kwh. Today, fossil-fuel generation is equivalent to between 0.8 and 0.9 lb-coal/kwh. But since about 10% of the power is hydro-electric today the overall result is between 0.7 and 0.8 lb-coal/kwh. This makes today's electric generation about 8 times more efficient than in 1900.
In 1900, the electric railways generated most of their own power instead of purchasing it from central power stations. So the next sections covers railway-owned power stations while the section after that covers central power stations. Since certain data about electricity generation by central power stations, is absent from the data for electric railways, it's important to examine both types of power generation. After about 1923, the electric railroads purchased most of their power from central power plants, etc. See [Stat. Abstract 1930]. By 1927, 68% of power was purchased.
For 1900, I estimate 6.0 lb-coal/kwh for such power stations. This estimate is obtained from estimates using [Census-1912] for 1902. Based on the amount paid for "hired power" and compared to the cost of generating their own power, it looks like about 85% of electric railway power was self-generated. So we need to find the lbs-coal per kwh for this generation (and assume that the efficiency of generation of purchased power was about the same). While the census data gives the kwh generated it doesn't give the amount of fuel used but only the amount paid for the fuel. So use the price that the Central Electric Light and Power Companies paid for coal ($2.06/ton, calculated) and assume that the electric railways paid the same. This gives 5.5 lb-coal/kwh. To bring this figure to 1900 (from 1902), add 0.4 per linear interpolation, resulting in 5.9. See [Ayres]. Using linear interpolation on the 6.85 figure reported by Ayres results in 7.25 lb-coal/kwh for 1900 (coal fueled central power plants) and not 5.9. But the 7.25 figure ignores hydro-power so "compromise" at 6.0
The discrepancy (between 7.25 and 5.9) may be in part due to:
1. Some of the generation by the railways was by hydro-electric which
resulted in less coal consumption. In this case, the electric
railways get credit for hydro-power. Except that if purchased
power) had a higher hydro content, it's not accounted for here.
2. The electric railroads may have generated power more efficiently than the Central power stations. The amount of power generated by the electric railways was about the same as by the central stations, so one can't use an "economy of scale" argument to imply that central stations should be more efficient. Since the electric railroads were a newer industry than central power stations, they may have had more modern (and more efficient) generators.
Note that if we accept the 7.25 figure (no hydro) and assume that 1/3 of the energy was generated by hydro-electric power (the estimate for central power stations see the next subsection), then the result is 4.8 lb-coal/kwh. So using 6.0 implies that the use of hydro power by the electric railways was less than average. But this seems logical since the primary business of electric railroads was not to generate electricity. So they likely were less likely to develop hydro resources than those whose only business was to generate and sell electricity. Industrial users that needed cheap electricity would be expected to locate where cheap hydro-power was plentiful but electric railroads had to locate where people needed transportation.
Another dilemma is this. Is it fair to count hydro so as to increase the energy-efficiency statistic? One could ask: How much coal would have been saved had there been no electric railways? Good sources of hydro power are limited and thus the existence of the electric railway doesn't stimulate the development of hydro power by all that much. If the electric railways hadn't existed, then there would have likely been a higher percentage of electricity generated by hydro. Thus would have resulted in a savings in coal well beyond that saved by electric railways not consuming coal via electric power. In the short run, if an electric railway decreases it's load, then the reduction in generation will come entirely from coal power, since hydro generation is almost free (once it's in place). There's no clear answer to this dilemma but the estimate of 6.0 lb-coal/kwh does take hydro into account (although perhaps not fully as explained above).
The "central power stations" included locations where hydro-electric power was generated. They didn't include generation by non-electric companies such the electric railways.
For the efficiencies of electric power generation (given in terms of energy-intensity and called a "heat rate") see Historical Statistics of the United States, Colonial Times to 1970, by the U.S. Bureau of the Census, Washington DC, 1975. Table S 95-107. This only goes back to 1920 and fails to show the heat rate for 1920-1924, but this may be estimated from other data in this table. Coal was the dominant fuel in the 1920s and the pounds(coal)/kwh is shown for 1920 onward.
Before 1920, an estimate for 1900 is in [Energy in Am. Economy] p. 180 (bottom). For 1900, it claims 6.85 pounds(coal)/kwh, but there's no explanation of how this was derived. The same figure is shown for 1902 in: [Ayres] p. 139, Fig. 1. This shows lbs/kwh as a graph between 1902-1950. Again, no source is given but the 1902 date is a dead giveaway that it's estimated from the 1902 Census data. So if it's 6.85 for 1902, linear interpolation would give 7.25 for 1900.
Another source for 1902 is "Entering the Seventh Decade of Electric Power" by C. E. Neil in the "Edison Electric Institute Bulletin", Sept. 1942, p.6. He claims a heat rate of 92.5K BTU/kwh which gives 7.06 lb-coal/kwh using 13.1 kBTU/lb-coal. It's about the same as Ayer's 6.85 figure and likely from the same source.
In the census data for central power stations: The tons and cost of coal burned is shown. For other fuels, only the cost is shown so that one may make an estimate of the BTU by assuming a price per BTU equal to that for coal. Since coal fuel dominates, errors for the other fuels are not all that harmful. Another major problem is that the aggregate kwh shown includes both hydro and steam generated power. What percent is hydro?
In the census of "Electric Light and Power Stations" the installed capacity is shown for both hydro and steam generation. If one assumes that the split between hydro and steam is 24% vs. 76% (directly proportional to the installed capacity for 1902) then one obtains a heat rate of 5.9 lbs/kwh for coal. This assumption for the split is likely erroneous since steam is used for peak loads. Much of the steam capacity would only be used during the evening peak loads while hydro might be better utilized (except for drought periods). Peak loads then were likely more extreme than they are now since there was a higher preponderance of lighting which mostly happened in the evening hours. In order to get the 6.85 lbs/kwh for coal plants, 34.4% of power generation should be hydro (not 22%). This implies (for central power stations) that the utilization of the installed steam generating capacity was only 60% of that for hydro. This may be reasonable since the generators (both hydro and steam) only generated 23.5% of what they would have, had they been generating 24 hours/day at full capacity (assuming a 90 % efficiency of converting mechanical work to electricity since the installed capacity was given in horsepower and not in kilowatts).
In 1900, the electric railways got about 7.5 pass-mi/gal  and the steam railroads perhaps 5.7 . A weighed average (based on distance traveled) gives 6.3 pmpg (harmonic mean). See  and [ICC-Graph] for distance.
For 2000 TEDB implies about 35 pass-mi/gal for the auto (using 124 k-BTU/gal). Small trucks (including SUVs) got 28.2 pmpg. Taking the harmonic mean (weighted by distance traveled) results in 32.7 pmpg for passenger transport in autos, SUVs, and small trucks. See Highway Statistics 2001, Table VM-1 Since 32.7 pmpg for autos in 2000 is about 5 times 6.3 pmpg in 1900, energy efficiency today is about 5 times better than in 1900 (neglecting non-auto modes for 2000). But including the non-auto modes doesn't change things much, as will be explained shortly.
For air, see . which estimates 38 PM/gal for 2000. Note that per [TEDB] Ed. 22, Table 2.11: "Passenger Travel and Energy Use", PM by air is about 1/8 of that by auto-SUV-air so take the harmonic mean weighted average of 38 PM/gal for air and 32 PM/gal for auto-SUV yielding 33.3 PM/gal for auto-SUV-air.
General aviation (private planes) per TEDB only gets about 9.5 pmpg but only constitutes 0.6% of intercity travel per [Trans in Am.] Intercity bus travel is claimed to obtain almost 130 pmpg and provides 2.2% of intercity travel. But the weighted harmonic mean of these is 35pmpg which implies that these two almost cancel out each other.
Since rail and bus transit, as well as Amtrak, get roughly the same pmpg as the auto (at 35 pmpg), little is changed by taking them into account. Urban buses only get about 26 pmpg while Amtrak got about 41 pmpg but only constitutes 0.6% of intercity travel. In 2001, Amtrak energy-efficiency declined by nearly 20% mainly due to much higher electricity use.
So the final resulting energy-efficiency today comes out to be 33.4 PM/gal which is a little over 5 times the 6.3 PM/gal estimated for 1900. Of course, one could say "roughly 5 times" since the estimates used for 1900 are rough and the "5 times" depends on these estimates.
See Census 2000 for the 2000 population figure. See Population (PBS). Or see Statistical Abstract of the U.S. The population went from 76 million in 1900 to 281.4 million in 2000, an increase of 3.7 times. The 4 used is thus high by 8% but is easy to remember. Since other estimates could be off by perhaps 8%, using 4 may not be as erroneous as it otherwise would seem to be.
For 1900 travel was 210 miles/year on steam railways [ICC-Graph]and perhaps another 130 miles by electric railways . That sums to 340 miles by rail. Today it's 16,000 miles a year  mostly by automobile and airplane, about a 50-fold increase over the 340 miles by rail in 1900.
This it obtained by two different methods. The first method reasons that since there is 50 times more travel per person and 4 times more people we travel 200 times as much (50 x 4 = 200) but since we are 5 times more efficient" then 40 times as much fuel is used (200/5 = 40).
The second method directly estimates the fuel consumed for passenger transportation for both 1900 and 2000. It's not used in the main body of this article, but is mainly used as a sanity check on the above estimate of "40 times". The result turned out to be 40.8 times but the methods used to find this need to be refined which may result in a number further away from 40.
For 2000, using [TEDB] Edition 22, table 2.11: Passenger Travel and Energy Use we add up the numbers and get 17,334 trillion BTU for 2000 after correcting for the low airline BTU by using the 2,336 trillion BTU for certified route airlines from said TEDB table 12.1 (table 9.2 in later editions): "Summary Statistics for U.S. Domestic and International Certificated Route Air Carriers (Combined Totals)" (corrects both for TEDB's under-counting of fuel used for international flights and counting fuel used for cargo as being used for passengers).
For 1900 The problem is more difficult. The railroads didn't segregate their fuel by freight and passenger service until about 1916. We only know from [Bukovsky] Table 3. that about 63.5 million tons of coal (including fuel oil equivalent) was used for both freight and passenger service. Now if we knew both the percent of coal used for passenger trains and the percent of passenger train fuel used for passengers (some was used for mail and express) then we could find the amount of coal used for rail passenger transport.
One crude way to do this is to assume that the ratio coal-pass/coal-freight is directly proportional to pass-mi/ton-mi. Here coal-pass means the tons of coal used for passenger trains, with coal-freight being the tons of coal used for freight trains and yard switching. Let this coal-ratio be equal to k times the pass-mi/ton-mi ratio. Then using the year 1916, find k. Using this same value of k and the known pass-mi/ton-mi for 1900, find the coal-ration for 1900. This coal-ratio will then make it possible to split up the total coal used in 1900 (63.5 M tons) into freight and passenger coal.
How valid is this method? It may be better to use car-mi ratios for passenger and freight cars if such data can be found. But the above method would be valid if coal-pass is directly proportional to pass-mi and coal-freight is directly proportional to ton-mi. In other words coal-pass = a x pass-mi and coal-freight = b x ton-mi. Here a and b are constants of proportionality and k = a/b. As efficiency improves, a and b will get smaller, but if freight and passenger service improve at the same rate, then k will remain constant, which is what we want since we hope that k for 1900 is about the same as k for 1916. If due to depression passenger traffic drops, or if it raised due to wartime, then the load factors (percent of seats sold) will change and k will vary too much. That is, constant a will change more relative to constant b which will likely change in the same direction but this results in a change to k. The years 1900 and 1916 are hopefully both fairly normal years.
Using the about method and the year 1918 to find k instead of 1916, the result is about 15.6 M tons of coal-pass for 1900. 1918 is not a good year to use but [Bukovsky] doesn't provide data for this prior to 1918. It seems that the ICC collected fuel data from various railroads but then neglected to add up the numbers to get totals. This may be such a case. Then if 80% of car-mi are passenger cars (20% mail and express cars) then we have 12.5 M tons of coal for rail passenger transport. The 80% is just a guess since it was about 72% in 1936. The above estimation need more refinement.
For the electric railways in 1900 we have [Census-1912] showing 4.82 M tons of coal consumed by electric railway power plants. But this needs to be increased due to net purchases of electric power by the electric railways from outside sources. See  which results in 5.05 M tons. To reduce this number to 1900 (from 1902) it should decrease by 8% due to less use of electric railways but should increase by about 10% due to less efficiency of power generation giving 5.15 M tons.
So adding 12.5 (steam rail coal) and 5.15 (electric railway coal) gives 17.65 tons of coal for passenger transport in 1900, Converting to BTU using 24M BTU/ton gives 424 trillion BTU. The figure for 2000 (17.3 trillion BTU) is 40.8 times larger. This is close to the 40 times estimate of the first paragraph of this section obtained by quite different methods. Some of the data used for this section was read from a graph [ICC-Graph], and could be in error by a few percent, so better data is needed but the results do tend to support the assertion that toady we use about 40 times as much fuel (in BTU terms) for passenger transportation as in 1900.
5. (not used)
The average travel distance is pass-mi divided by the population in 1900. To get pass-mi, multiply the estimated pass-mi/kwh (4.5)  by the kwh used. Unfortunately, the electric railway census data for 1902 [Census-1912] only gives the kwh generated, ignoring the kwh purchased and the kwh sold. Electric railways often sold some of the power they generated. But the census does show the cost of kwh purchased and the revenue from kwh sold. If one can estimate the price (per kwh) for buying and selling, then one can then find the number of kwh bought and sold. Then kwh (used) = kwh (generated) + kwh (purchased) - kwh (sold). The estimate using the above method is (in billion kwh): 2.37 (used) = 2.26 (generated) + 0.34 (purchased) - 0.23 (sold). Note that most of the power was generated so that errors in estimating the prices are not all that significant.
For the selling price assume that the electric railways sold power for the same price that the central power plants charged (on average). This was 3.34 cents/kwh and included all types of customers. For purchasing electricity, assume that they paid 30% more than the operating and maintenance costs of self-generation or 1.18 cents/kwh. The 30% is added to account for capital and administrative overhead. Since the electric railways were big customers, it seems reasonable that they would be able to purchase power at about half the price that they sold it for (mainly to commercial and residential customers). More research is needed on this.
The result of the above is (4.5 PM/kwh x 2.37 Bkwh)/76 M (population) = 140 miles/year per person of travel by electric railways but this was for 1902. Streetcar ridership was then rapidly growing and nearly doubled between 1890 and 1902. See "Proceedings of the Federal Electric Railways Commission" U.S. GPO 1920, vol. 3 p. 2223, Chart C-107: "Riding Habit". Linear interpolation would decrease the 140 by 8% to make it valid for 1900. This gives 129 miles/year (about 130). The Pass-mi for 1900 then comes out to be 9.8 billion (about 10 billion).
As a sanity check on this indirectly estimated value note per "Riding Habit" that in 1902 the typical person made 61 trips on electric railways. Dividing 140 miles by 61, results in an average trip length of 2.3 miles. For 1900, it would be a little less, say 2.0 miles. This figure seems reasonable considering that most of the lines were short city streetcar lines and not interurban lines.
The following estimate indicates that roughly 14% of the line length was interurban in 1900. [Hilton] p. 186: Table 6 "Statistics of Electric Interurban Railways 1889-1959" shows 2,107 miles in service in 1900. Compare this to the 21,902 miles of track for electric railways (both urban and interurban) in 1902 (see [Stat. Abstract 1930]) Assume it was 20,000 in 1900, based on linear interpolation of the total miles of track operated between 1890 and 1902. Since it's claimed that conversion to electricity was mostly complete by 1900 the change from 1900 to 1902 mostly represents construction of new lines (and not conversion of horsecar lines to electricity). Also note that in 1907 at least 2/3 of the line length was single track. [Stat. Abstract 1930] If the percentage of single track was the same in 1902, this implies that the 20,000 miles of track represented at least 15,000 miles of line. So only about 14% of the line mileage was interurban in 1900. (Is there better data in [Census-1912]?)
The above has estimated a statistic for 1902 that in 1902 was thought to be unknown. From the 1902 version of [Census-1912] p.9 it states: "It is quite possible that taking all street railways together, the passenger mileage, or number of passengers carried 1 mile, per mile of track operated, is larger to-day than it was in 1890, but statistics on this subject are wholly lacking."
The figure of 130 miles per person may seem low but in 1900 most people didn't live in cities that had electric railways and if they did, many didn't live near an electric railway line or didn't travel along the electric railway route or saved fares by walking or bicycling. See Population So most people who were actually using electric railways were using them much more than just 130 miles per year.
In 2000 the typical person traveled perhaps 16,000 miles. See Pocket Guide to Transportation by the Bureau of Transportation Statistics (U.S.). Table: Per Capita Passenger Travel and Freight Transportation. For the 1995 NHTS survey one may add local travel to long-distance travel to get about 17,500 but some of this is double counting. But the 2001 survey shows only 14,500 for "daily trips" See Bureau of Transportation Statistics | Daily Passenger Travel. This figure is too low as will be explained in the next two sections. The U.S. population is found in the Statistical Abstract of the U.S.
Another source is [TEDB]. Using Edition 22, table 2.11: "Passenger Travel and Energy Use" and correcting to include all international air travel on U.S. owned carriers per table 12.1: "Summary Statistics for U.S. Domestic and International Certificated Route Air Carriers (Combined Totals)" the result is about 16,000 miles/year per person. This is also roughly 50 times 340 miles (in 1900) = 17,000 miles. More precisely it's exactly 47 times but since the data isn't precise, it isn't much of an exaggeration to use 50 times. The correction for international air is needed since U.S. citizens often travel on foreign airlines for which no passenger-miles are reported (and the passenger-miles of foreigners on international flights of U.S. carriers was excluded). So all passenger-miles on U.S. airlines in international flights is allocated to the U.S. to approximately compensate for this under-counting.
The 14,500 miles per year for each person (on average) is based on people keeping a diary for a travel day and reporting it later on. One may login to the NHTS website (after registering) at ORNL Login to NHTS and run programs there to extract statistical data from the survey database. Doing this for "Commercial/charter airplane" for person-miles resulted only in 277 billion pass-mi by air for the 2001 survey. But [TEDB] (ed. 23) reports both 566 billion pass-mi (Table 2.11) and 665 billion pass-mi (Table 9.2) for 1991. This is the same situation reported on in the above section: TEDB calculation and correction using the same two tables in an earlier edition (but numbered differently in different editions). So the one-day diary trip logs missed nearly 60% of air travel attributable to the United States (includes about half of international travel by all people to-from the U.S.). Why?
For one, foreign visitors to the U.S. (who are apt to have flown here and also fly within the U.S.) are excluded from participating in this survey since they were not invited to participate. The survey was set up by first picking random residential phone numbers in the U.S., finding the address, and then sending a letter with a $5 cash incentive to invite people to participate. About 60% declined. Foreign residents who planned to visit the U.S. obviously were not so contacted.
Another source of error is that people were asked to report a long trip (over 50 miles away from home) only if they ended that trip within the 24-hour travel day. Many people may have erroneously thought that they only ended a trip when returning home and if the trip had multiple destinations they may have only reported the last leg of the trip (from the last destination to home). It they were returning from a trip to several destinations, they should have reported the entire trip, lasting perhaps many days, in their daily trip log but likely didn't.
A third reason may be that people who fly a lot are likely to be both very busy and have high incomes. The incentive money for them is peanuts. So they, like the majority of people, opt out. There are likely other reasons too.
So how should the 14,500 mile figure be corrected. Since there are about 4 trillion pass-mi per year estimated by NHTS, the additional 388 billion pass-mi by air that they missed increases the 14,500 figure by nearly 10% to almost 16,000 miles (actually 15,906).
But the reasons given why it's too low apply in some cases to highway travel. For example, don't foreigners travel around in rental autos and tour busses, etc. and remain uncounted? So the 16,000 estimate needs to be increased by an unknown amount. While the air discrepancy between NHTS and TEDB is high (TEDB is 140% higher), for road and highway travel TEDB is only about 8% higher. But while the error for air is clear since the data in TEDB was obtained based on actual passenger counts submitted by the airlines to the Bureau of Transportation Statistics, the TEDB road data is only based on estimates by states for vehicle-miles which the TEDB then converts to passenger miles using the occupancy estimates obtained by NHTS surveys. Thus the TEDB estimates are likely in error so one just doesn't know if the NHTS for passenger miles by road should be increased by say 4%, 8%, or 12%, etc. If we pick 4% and note that passenger travel via private motor vehicles is about 85% of total passenger miles, then we need to increase the 1600 estimate by about 3% to yield about 16,500 miles per year for each person (more exactly 16,446 using the 15,906 figure above).
So in summary the estimate of 14,500 miles per year travel per person in 2001 needs to be increased to perhaps 16,500.
8. (not used)
For steam rail [ICC-Graph] shows 48 billion PM for 1920 and 28 for 1930, a 20 billion PM loss. (about 40%). For the auto, [BusFacts-1935] shows a 350 billion PM gain from 60 Billion in 1920 (about a 6-fold increase). [Stat. Abstract 1930] shows little change in the number of electric railway passengers between 1917 and 1927 so assume that the pass-mi was the same in 1920 as in 1925. Then per [BusFacts-1935] electric railway pass-mi declined from 50 billion to 40 (a 20% drop) from 1925 to 1930. While the number of passengers didn't decline that much, interurban mileage declined by 32% over the decade (per [Hilton]) so the decrease in trip length accounts for much of the decline.
Using "Bituminous Coal Annual", 1948, p.116, table 51 gives car-mi per ton of coal. Then multiply by the ICC's data on passenger-miles per car-mi. Then multiply by 0.8 to account for car-mi of dining and baggage cars, etc. This is based on the same methodology as used in USA Railroad Passenger-Miles per Gallon 1936-1963
ICC's Bureau of Statistics, published an annual: "Revenue Traffic Statistics of Class I Steam Railways in the United States" (Statement M-220). Statistic Used: Passenger-miles per car-mile.
Also see USA Railroad Passenger-Miles per Gallon 1936-1963, Steam The results range from 8.0 PM/gal in 1920 (high due to crowded trains in the aftermath of World War I) to 5.4 PM/gal (low due to low ridership during the great depression).
Another source is: American Transportation in Prosperity and Depression by Thor Hultgren. National Bureau of Economic Research (NBER), Studies in Business Cycles, No. 3, 1948: p. 233, chart 94: "Passenger-miles per Ton of Coal or Equivalent Consumed in Passenger Service". This covers 1920-1940 and ranges from 1,400 in 1920 to 800 in 1933 with an average value of about 1,100. Equating a ton of coal to 200 gallons of gasoline results in 5.5 pass-mi/gallon on average. The range is 7 PM/gal to 4 PM/gal.
This gives a lower fuel-efficiency than the method based on ICC which is likely due to not subtracting the roughly estimated 25% share of fuel used to transport mail and express freight on passenger trains (based on car-mi of "other" cars). But increasing the PM/gal by 33% (1/0.75 - 1) to account for this results in values that are somewhat higher than those by the 1st method.
The same statistics supposedly used by Hultgren (but not the same values) are found at the website: NBER statistics: Transportation and Public Utilities http://www.nber.org/databases/macrohistory/contents/chapter03.html. The figures here have significantly wider variations from month to month than in Hultgren's book. The chart by Hultgren seems to be plotted with data points for every month, which implies that there should be no discrepancies in the data. But for some months one set of data may be 20 % higher than the other set. For other months it's just the reverse. For some months they almost agree. Could Hultgren have used a "moving average" where the value shown for each month is an average of values for previous months?
See also: [Bukovsky] p. 72, chart V: "Rates of Consumption of Fuel and Power by Locomotives and Rail Motor-Cars - Class I Line-Haul Railways, 1916-1943". Data for this chart comes from Table 19 on p. 70. This shows a decrease in energy-intensity from 18.1 lbs-coal per passenger car-mi in 1923 to only 14.7 in 1930, a decrease of 4.4 over 7 years. But between 1916 and 1923 it went 18.5 to 18.1, a decrease of 0.4 over 7 years. 1916 is the earliest year covered. It seems that prior to 1916, fuel statistics were not gathered separately for freight and passenger service.
The 1900 estimate is obtained by extrapolation from data of 1916 and later years. For 1900, assume that the energy intensity was 20 lb-coal per car-mi and that there were an average of 15 persons/car. This is equivalent to 6 pass-mi/gal (after multiplying by the 0.8 factor).
The estimate of 20 lb-coal/car-mi implies a decrease of 1.5 lb-coal/car-mi over 16 years from 1900 to 1916. Compare this with the decrease of 3.5 lbs-coal/car-mi over 27 years from 1916 to 1943. The 1.5 figure is conservative and may overstate energy-efficiency in 1900.
The estimate of 15 persons/car is also based on extrapolation based on data from after 1916. Between 1920 and 1935 the persons/car decreased from 19.76 (wartime conditions) to 10.93 (depression conditions). In 1925 it was 14.78 and in 1916 it was 15.50. Also, the typical size of the cars was smaller in 1900. The pass-mi/car-mi is multiplied by 0.8 to account for the dining and baggage cars, etc. Conversion between coal and gasoline is at 9.3 lb-coal per gal of gasoline. The result is 5.7 pass-mi/gallon for 1900.
Prior to 1940 there is no survey data. However, there is a lot of anecdotal reports, many of which are on the Internet. A major problem is that some of these are taken from advertisements by the auto makers and thus are suspect for being hype. Also, examples that people mentioned in print likely tend to be from people who were bragging about what good mileage they got. They were likely from people who took better care of their cars and drove better so as to get better mileage than the typical driver.
1900-1910: The Antique Automobile Club of America has a website which claims 35 mpg for 1900. For the 1903 Cadillac (10 hp, 1 cyl., max speed 30 mph), 25 mpg is claimed. Roads were mostly dirt which contributed to poor economy. So in the early years of the auto it could be 20 mpg, about the same as a hundred year later (2000).
1910-1930: Per Antique Automobile Club of America: 20 mpg for 1919 and also for the Ford model T. But a website by UAW Local #387: www.local387.org/ford_model-t.htm says it was 13-21 mpg for the model T (from 1909 to 1927). This seems more realistic. Since Ford was considered to be more economical than average, it seems that for the 1910-1930 period it was under 15 mpg. In 1915 a Studebaker got 13 1/2 mpg coast-to-coast over the gravel Lincoln Highway, but other cars did worse (Studebaker News, Oct. 1915).
1920-1950: see [Ayres]. He claims p. 131 that the mi/gal for automobiles has shown no improvement from 1920-1950. But he suspects that there was higher automobile occupancy in earlier times. He claims on p 132 that "Statistics on miles per gallon are unreliable and confusing." He says that the records of car fleets show lower mi/gal than national mi/gal estimates.
1940-1955: [Energy in Am. Economy] p. 656, Table D-37 which shows per the Bureau of Public Roads (in car-mi/gal): 1940: 15.3, 1945: 15.0, 1950: 14.5, 1955: 14.5. Also reported here are somewhat higher estimates by someone from General Motors in a 1957 paper.
1940-2000: U.S. DOT: Federal Highway Administration: Highway Statistics. See issues for 1985, 1995, etc. that summarize previous years. For example: "Highway Statistics, Summary to 1985 pp. 229-232 Table "Annual Vehicle-Miles of Travel and Related Data 1936-1985". The "data" is obtained by estimates from individual states and there is apparently a lag of a number of years before improvements in fuel-efficiency fully show up in the tables. This is because states sometimes use fuel consumption figures to help estimate vehicle-miles, using the mpg figures reported in highway statistics. If all estimates of vehicle-miles were made based on fuel sales, then all changes in fuel-consumption would be erroneously attributed to changes in the number of vehicle-miles (and not to changes in mpg). Then the mpg figure reported would never change (even though actual mpg did change). It's of course not this bad, but this explains the reason for the delay. The dramatic improvement in mpg in the mid and late 1970's didn't show up in the statistics much until the 1980s.
1970-2000: See [TEDB] The BTU/PM for automobiles prior to 1990 are too low due to using the erroneous data on automobile occupancy supplied by NPTS  I believe that there hasn't been much change in automobile occupancy since the 1970s so use the figures on BTU/vehicle-mile for trends over time. See  To get pass-mi, multiply by the persons/car (average). Today it's about 1.6. In the past it was likely higher but not nearly as high as claimed by NPTS due to double counting as explained elsewhere. If it were 1.67 (1 2/3) in the 1950s the result would be about 25 pass-mi/gal.
This is found in [TEDB] Ed. 23, Table 2.13: "Energy Intensities of Nonhighway Passenger Modes". In earlier editions prior to ?, highway and nonhighway were combined into the same table.
One jump in Amtrak energy intensity happened when TEDB Ed. 21 was released in 2001. Prior to that, TEDB allegedly failed to properly account for the heat lost in electricity generation. Robert Cote, per his email posting of 16 June 2002, reported this error and TEDB corrected it, correcting all values back to 1995.
A even larger jump is reported (in TEDB) for Amtrak energy-intensity in 2000-2001-2002, but was later retracted. It went from 2,902 BTU/pass-mi in 2000 (per Ed. 22) to 4,137 BTU/pass-mi in 2001 (per Ed. 23) to 4,830 BTU/pass-mi in 2002 (per Ed. 24). Ed. 23 was modified to show 3,356 for 2000. However Ed. 24 retracted these sharp increases and showed 3,105 3,114 and 3,268 BTU/pass-mi for 2000-2002 (not much of a jump).
So what caused this? Was there really a jump or just an accounting error. And why the error? Look at Table A.16 in Ed. 23: Intercity Rail Fuel Use. It shows a jump in electricity use from 470 M kwh in 2000 to 817 M kwh in 2001. But Ed. 25 shows a drop from 470 M kwh in 2000 to 456 M kwh in 2001 but up to 518 M kwh in 2002. Why was this? Look at Table A.15 in Ed. 24 and note that from 2001 to 2002 there was almost no change in electricity use, but a change in diesel fuel use from 96.8 to 115.7 million gallons. This accounts for the 2001-2002 jump in BTU/pass-mile. Train car-mi only went up 2% in 2000-2001 so more trains don't account for the reported increase in electricity use.
Was one possible accounting error due to erroneously allocating electricity that Amtrak may sell to commuter lines as being used by Amtrak? If so, that doesn't explain the diesel fuel error. Could the electricity discrepancy have something to do with the introduction of the inefficient Acela train sets? It's not clear what happened and needs looking into.
Sources of "statistics":
1935-1955: [Energy in Am. Economy] p. 550
1950-1970: [Hirst] pp. 9, 21, 34-5
A major problem is how to allocate aircraft fuel between freight and passengers since passenger flights often carry mail and freight (other than the baggage of passengers). [Hirst] p. 35, considered 400 lbs. of mail/freight equivalent to one passenger. This may be too low so I've used 500 lbs. (or 4 passengers = 1 ton cargo).
Thus to find BTU/pass-mi, one adds the reported passenger miles to 4 times the cargo ton-miles to get equivalent-passenger-miles and then divides this into the total energy use in BTU to obtain the BTU/pass-mi. All these input statistics of the previous sentence are found in "Table (9.2 for ed. 26): Summary Statistics of U.S. Domestic and International Certificated Route Air Carriers ..." in Transportation Energy Date Book TEDB. In 2000 this implied that reported (by TEDB) BTU/pass-mile needs to be decreased by 17% (about 20% for 2005).
"Energy in the American Economy" has an erroneous Table D-51 (p. 667): "Miles per Gallon in Passenger Service of Domestic Scheduled Air Carriers". It wasn't used due to its failure to account for aircraft fuel used for cargo and mail transport by both cargo and passenger aircraft. The same error was made by TEDB. If one uses [TEDB], edition 22, 2002, table 12.1: "Summary Statistics for U.S. Domestic and International Certified Route Air Carriers" and assumes that one ton-mi of cargo is equivalent to 4 pass-mi one obtains the equivalent of almost 38 pass-mi per gallon of automobile gasoline for the year 2000.
In comparing the energy-efficiency of air travel with the auto, it should be compared with intercity automobile travel which is more energy efficient due to higher vehicle occupancy and higher vehicle miles/gallon.
In the table below, data for 1935-1955 is derived from [Energy in Am. Economy] p. 550, Table XXVI: "Petroleum Products Consumed Compared to Work Performed by Aircraft, Selected Years 1935-1955". It's assumed by me that one ton of cargo is fuel-equivalent to 4 passengers. All reported jet fuel use by this Table xxvi was disregarded, since per footnote c only an insignificant amount was used by "scheduled air carriers" (most of jet fuel was likely used by the military). The high efficiency for 1945 was due to planes being full due to wartime conditions. International flights were significantly less energy-efficient than domestic prior to 1955, but by 1955 there was only a little over 10% difference.
Heat values for aviation gasoline: 120.2 k BTU/gal and for jet fuel (kerosene): 135 k BTU/gal. Both of these are from [TEDB], edition 22, 2002, table B.3: "Heat Content for Various Fuels"
Passenger-Miles per Gallon and BTU per Passenger-Mile
PM/gal is shown for both aviation gasoline (lower number) and the equivalent automotive gasoline (higher number) for comparison to auto fuel economy.
Scheduled Domestic | Scheduled International per David Lawyer | per David Lawyer (gasoline) l (gasoline) PM/gal PM/gal BTU/PM | PM/gal PM/gal BTU/PM 1935: 12.3 12.8 9,770 | 7.6 7.9 15,820 1940: 16.8 17.5 7,150 | 11.7 12.2 10,270 1945: 27.5 28.6 4,370 | 19.8 20.6 6,070 1950: 21.0 21.8 5,720 | 16.5 17.2 7,280 1955: 23.3 24.2 5,160 | 20.9 21.7 5,750 per Eric Hirst | 1955: 25.0 26.0 4,800 | Hirst used 1 ton = 5 passengers. 1960: 17.4 18.1 6,900 | Note the discrepancies for both 1955 1965: 14.7 15.3 8,200 | and 1970 due to different authors. 1970: 14.3 14.9 8,400 | per TEDB for both Domestic and International (after correcting for 1970: 13.4 13.9 8,980 fuel for cargo using 1 ton = 4 passengers) 1975: 18.5 19.2 6,510 1980: 25.8 26.8 4,660 1985: 27.4 28.5 4,390 1990: 29.2 30.4 4,110 1995: 34.2 35.6 3,510 2000: 36.4 37.9 3,300
Note that aviation gasoline was phased out during the period centering around 1960 and replaced by kerosene jet fuel which has a higher heat value (135k BTU/gal for kerosene vs. 120.2k BTU/gal for aviation gasoline). The above table continues to use PM/gal (aviation gasoline equivalent) long after aviation gasoline was replaced by kerosene. To abruptly switch to kerosene for the PM/gal values in say 1965 would have caused a deceptive jump in the time series so this wasn't done. Another column could have been added for PM/gal (kerosene) but wasn't.
The 0 for the low-order digit of the BTU/PM is due to rounding so as to retain 3 significant figures. Eric Hirst has 00 for the last two digits and thus only retains 2 significant figures. Due to the uncertainties of allocating fuel to cargo transport, keeping only two or three significant figures is reasonable.
The reason why international flights were less energy-efficient than domestic flights prior to 1955 is because long distance non-stop flights (such as trans-oceanic international flights) must carry a huge load of fuel. On a long flight, the weight of the fuel needed for each passenger may weigh several times as much as the passenger. Today, due both to higher load factors on international flights and longer domestic flights, there isn't much difference in energy-efficiency between international and domestic flights. In the early days of aviation, domestic flights often made intermediate stops for refueling which reduced fuel use due to lower fuel weight while airborne.
TEDB has also made a mistake by only counting half of the fuel used by U.S. airlines in international service as well as only counting half of the international passenger-miles on such flights. This give reasonable results for calculation energy-efficiency but give results that are too low for both fuel use and passenger-miles by air attributable to the United States. This is because no statistics at all are taken for foreign airlines that serve many U.S. international airports and U.S. citizens fly on these airlines.
If other countries calculated their statistics the same way as TEDB did, then they would exclude half the fuel used on their international flights. Then summing up these statistics for all countries in the world for airplane fuel, would leave out half of the fuel used for international flights. The violates the basic principle that summing the statistics of all countries in the world should give the total world consumption. All aircraft fuel used by the airlines of the world needs to be fully allocated to individual countries.
Note that per Table of BTU/Pass-mi energy intensity increased after 1955 from about 5k BTU/PM to about 9k BTU/PM in 1970. This was mainly due to the introduction of inefficient "jet" aircraft. But after 1970 the energy intensity decreased to less than it was in 1955, due in large part to the introduction of turbofan engines with high bypass ratios.
The word "jet" regarding passenger aircraft is actually a misnomer. While some military aircraft use turbojet engines, most passenger commercial aircraft today use turbofan engines. Although people call them "jets", they are similar to propeller craft where the propellers are concealed from view and are called "fans". A gas turbine, powered by kerosene, drives a large fan which surrounds the turbine and throws air out the rear of it, pushing the plane forward much like a propeller. Some of the "air" thrown back is exhaust gas from the turbine, but most of it is just plain air. This air bypasses the turbine and is not used for combustion. It just flows backwards around the outside of turbine. The bypass ratio is the mass of the bypass air to the mass of the air used for combustion. So an engine with a high bypass ratio will have a high volume of air go thru the fan and will be more energy-efficient as will be explained later.
Originally, passenger "jet" aircraft were turbojet but by the early 1960s, turbofans with low bypass ratios were being introduced. For example, early Boeing 707's were turbojet but later 707's were turbofan. The introduction of low-bypass ratio turbofans and then increasing the amount of air bypassed (high-bypass ratio) resulted in later models "jet" aircraft being much more energy efficient than earlier models. Some additional improvement was obtained by by increasing compression ratios,
Why are high-bypass-ratio turbofan engines more efficient? We'll take a simplified example where an airplane is flying in level flight at constant speed thru still air (no natural winds). This airplane shoots out a mixture of exhaust gas and air from its turbofan engines, leaving a mixture of air and exhaust moving backwards, which we'll just call exhaust. Now the kinetic energy of this exhaust is just the mass of it times one-half of the square of the velocity (to an observer looking up from the ground). All this kinetic energy of the exhaust in the sky moving backwards was supplied by the kerosene fuel. Cut this velocity in half and you reduce this energy loss by a factor of 4 (due to the v-squared law where v is velocity).
Except there's one problem if this velocity is halved. The airplane always sees the velocity of the air entering the engine from the front as equal to the speed of the airplane. The thrust force generated by acceleration of air in the fan (and in the turbine too) is the air flow (in kg/sec) times its change in velocity (as viewed by an observer in the plane) and if you think about it, this change is just equal to the exhaust velocity as viewed by an observer on the ground. So if you halve the velocity of the exhaust you halve the change in velocity (between intake and exhaust) as viewed by an observer on the airplane and thus halve the thrust force. But thrust force must be maintained so as to maintain speed (or climb). Thus if one cuts in half the velocity change, one must at the same time double the exhaust flow to keep thrust constant. This doubling is done by increasing the bypass ratio.
The doubling of exhaust flow doubles the wasted energy in the moving exhaust air. But remember that halving the velocity has decreased the this energy by a factor of 4 so the overall result is cutting in half the wasted energy of the moving exhaust in the sky.
Note that the fuel consumption has by no means been cut in half. There is still a lot of air being directed downward by the wings so as to push up on the wings to keep the plane from falling out of the sky. And there is air being pushed forward as the front of the aircraft hits the still air. So why did high bypass ratios make such a big difference? It was because the ratios were greatly increased and the velocity was reduced much more than in the example just presented
The above example is overly simplistic as it has neglected the part of the exhaust that represents the kerosene fuel (the carbon and hydrogen components of the exhaust in the compounds of carbon dioxide and water). But carbon and hydrogen constitute only a few percent of the exhaust (for bypass ratios greater than one) and can be neglected in a rough example.
For an interesting history of the turbofan aircraft engine see: Jets Fans, Dec. 2003
See [TEDB] The TEDB figure indicates (for 1990's) that the auto is more fuel-efficient than transit while showing intercity rail to be much more efficient than the auto. Both of these are misleading. Splitting the auto data into 2 parts (urban and intercity) will show that the auto is roughly the same energy-efficiency as mass transit and intercity rail.
My estimation for autos uses: miles/gal: urban 20, intercity 26; persons/auto: urban 1.4, intercity 2.0. BTU/gal is 125,000. This gives: urban 28 PM/gal; intercity 52 PM/gal; average 35 PM/gal. Note that intercity is about 50% higher than the average value of 35 PM/gal.
These numbers are estimated based on:
1. For mi/gal: EIA estimates about 22 mi/gal in a recent pamphlet [TEDB] used 21.6). "Highway Statistics, 1990" by FHA, DOT in table VM-1 shows about 1/3 of vehicle-miles is non-urban. Looking over EPA tables of mi/gal leads to the estimates of 20 (urban) and 26 mi/gal (intercity) which averages to about 22 when weighted by urban/intercity vehicle-miles. The "average" should actually be done by using the harmonic mean method but the error introduced by a using the arithmetic mean is small compared to other errors.
2. For persons/auto the "1990 Nationwide Personal Transportation Survey" (NPTS) by FHA, DOT (p. 7-5) shows 1.62. pass-mi/veh-mi for autos. Using a figure of 1.6, this could be split up into 1.4 for urban and 2.0 for intercity similar to the above. This split is based on the following:
Old (1970) studies for Los Angles and San Francisco give persons/auto as 1.44 (studies agreed). For work trips, the Los Angeles study showed 1.10 persons/vehicle while for the entire U.S. this figure was 1.17 (U.S. Census of Population 1970). For 1990 the U.S. figure is 1.10. So one may reason that Los Angeles was 20 years ahead of its time regarding auto occupancy and that the rest of the nation in 1990 was about what Los Angeles was in 1970. So this implies that one might use 1970 data for Los Angles to approximate what the U.S. was in 1990. Doing this gives an occupancy of 1.44 which is rounded to 1.4 since: 1. Such reasoning is only a crude estimate 2. The author has personally sampled occupancy and thinks that 1.44 may be too high.
3. Using 1. and 2. above and 125,000 BTU/gallon for gasoline gives:
overall auto BTU/PM = 125,000 / (22 x 1.6) = 3,550
intercity auto BTU/PM = 125,000 / (26 x 2.0) = 2,400 (about 33% lower)
urban auto BTU/PM = 125,000 / (20 x 1.4) = 4,460 (about 25% higher)
Note: only 3 significant figures used so as to make last digit zero. The overall figure is about the same as the 3,543 BTU/PM reported by [TEDB] for 2000.
A 1979, study by DOE estimated 2,810 BTU/PM for the intercity auto in 1976. See House Committee on Appropriations for the Federal Railroad Administration, Amtrak. Thursday March 22, 1979, Section: "DOE Statistical Report" (p. 848). It also shows Amtrak at 3,230 BTU/PM (worse than the intercity auto).
USA Railroad Passenger-Miles per Gallon 1936-1963 by David S. Lawyer (the author)
See: [Trans in Am.] "Intercity Travel by Modes". In 1955, rail had only 4.0% of the intercity travel market. Per "Yearbook of Railroad Facts" (annual). Association of American Railroads, in 1955 there were about 6000 steam locomotives vs 31,500 diesel-electric units. By 1960, there were only 261 steam locomotives in service.
For the fuel-efficiencies see: "Amtrak and Energy Conservation in Intercity Passenger Transportation" by Stephen J. Thompson (Congressional Research Service, Report to Congress) Sept. 3, 1996. (http://www.cnie.org.nle/eng-11.html) See also [TEDB]. This shows the energy of Amtrak to be only about 8% better than the automobile (for 2000). Note that in 2001 per [TEDB] Amtrak's fuel efficiency significantly dropped making the auto about 15% more energy efficient.
But the automobile figure used in the above is for both city and intercity driving. To fairly compare it to Amtrak, one must correct the auto figure so it reflects intercity use. For intercity, there are about 2 persons/auto as compared to 1.6 overall, and the auto (in intercity use) gets more miles/gallon (about 26 as compared to 22 overall).  After making this correction (by increasing the auto energy efficiency by nearly 50%), Amtrak is significantly less efficient than the auto for 2000 and even worse in 2001.
See also CRS Report 96-22 - Amtrak and Energy Conservation Background and Selected Public Policy Issues - NLE Abstract. or alternate site if above link broken This 1999 update by the Congressional Research Service, agrees with the above conclusion that Amtrak energy-efficiency is about the same as the auto. The Amtrak energy intensity they used from "Transportation Energy Data Book" was too low due to the failure to consider that each BTU of electricity takes a few BTUs of fuel to generate. This resulted in the energy-efficiency of Amtrak's electric trains being grossly overstated. At this same time, it looks like the energy efficiency of the automobile was also likely overstated since in 1970-7 the number of persons/auto was assumed to be 1.9 [TEDB] which seems to be too high . But while the data may be flawed, the conclusions of the CRS report turn out to be the same as mine.
Before 1860: The Transportation Revolution, 1815-1860 by George Rogers Taylor, (Vol IV of the Economic History of the United States) Holt Rinehart and Winston, New York, 1951: p.74 claims that in 1840 Europe had 1,818 rail miles vs. about 3000 for the U.S.. Table on p.79 shows rail mileage.
For steam railroads see American Railroads by John F. Stover. University of Chicago Press, 1961, p. 224, table: "Growth and Decline of Railway Mileage in the United States". See also Yearbook of Railroad Facts (annual), Association of American Railroads, Washington, DC., but it neglects early years.
For electric railways see Statistical Abstract of the United States, 1930, p. 422-3 tables: "Electric Railways: Summary of Operations" and "Electric Railways: Mileage ...". This shows 32,548 line miles for 1917 and 31,264 for 1922. For 1902 it shows 21,902 track miles, which I used to estimate 14,250 miles of line for 1900 using linear interpolation and a ratio of miles-of-line to miles-of-track of 0.75.
[Energy in Am. Economy] p.84+: "Oil, The Beginnings of the Industry".
For early wood burning locomotives see John H. White, American Locomotives, an Engineering History 1830-1880. Johns Hopkins Press, 1968. p.78 states that in 1838 the Long Island Railroad got 48 train-miles per cord of wood. The Boston and Providence got only 36mi/cord. p.71 indicates that the typical train weighed about 100 tons (including the locomotive). Using the ratio of the heat value of a ton of coal to a cord of wood (1.35) and using 4200 ton-mi/cord results in the equivalent energy-intensity of about 350 lb-coal/k-gross-ton-mi. The 1.35 figure is derived from [Ayres] p.317 (table: "Heat Value of Representative Solid Fuels") and p.323 (table: "Some Weight-Volume-Heat Value Relationships of Fuel Wood") using the average heat value for bituminous coal. See also [Energy in Am. Economy] p.51 (top) where it claims a ratio of 1.25 for "good hardwood" (but it could well be 1.35 for just average wood)..
350 lb-coal/k-gross-ton-mi in 1838 is about twice the value of 170 reported for 1916 and over 3 times the value of 110 reported for 1940. See [Bukovsky] p.72 Chart V: "Rates of Consumption of Fuel and Power by Locomotives and Rail Motor-Cars -Class I Line-Haul Railway, 1916-1943" curve label "Road Freight Service per 1,000 Gross Ton-Miles (Including Locomotives and Tenders)".
So what is the estimate for the steam engine thermal efficiency? Around 1940 it's estimated that steam engines were about 6% efficient. See . So in the 1830's they were likely under 2% efficient since they used over 3 times as much fuel per gross-ton-mi. However, since trains then went slower in olden days, they had less aerodynamic drag, so the 2% figure is likely too high and should be perhaps only 1.5%.
Steam engine efficiency thus improved over time, quadrupling between the 1830s and the 1930s. Using an assumed linear progression of efficiency from 1.5% in 1836 to 4% in 1916 results in about 2.5% for 1866 (near the peak of wood fuel use). The reason why all years end in 6 is because U.S. government data for this started in 1916.
Per [Energy in Am. Economy] p.59 in the 1850's a coal expert from England reported that ..., locomotives, ... were almost entirely supplied with wood. On p. 52 it states "Wood remained until about 1870 the principal fuel used by railroads." "... scattered references indicate that they [railroads] may have burned up to 6 million cords a year in the late 1860's." Per p.53 by 1879 (over 10 years later) the U.S. Census found that this figure had declined to only 2 million cords a year. See "The Forests of the United States in Their Economic Aspects", Census of Manufactures, Vol. 9, U.S. GPO 1879, p. 489. The 6 million cords was only about 5% of total wood burned in the US, estimated to be between 100 and 140 million cords per year, most of which was burned in fireplaces and wood stoves. See: [Energy in Am. Economy] p.52.,
See: American Railroads by John F. Stover; University of Chicago Press, 1961, p. 162. In the 1860s major railroads were switching from wood to coal as a fuel. Per p.62, there was 35,000 miles of railroads in the U.S. in 1865 (perhaps at the peak of the wood-burning era). But by 1900 the mileage had grown to 193,000 (see p. 224).
How many passenger-miles were by wood-burning trains in say 1865? While no statistics were gathered then, one may attempt to use miles of line as a proxy for pass-mi. So since there was 5.5 times more miles of rail line in 1900 as compared to 1965, estimate that there was also 5.5 times more passenger-miles. Then to find the ratio of pass-mi via rail in 1865 as compared to 1900. Steam rail travel in 1900 was 210 miles/person vs. 340 total (includes electric railways which didn't exist in 1865) (see 50 times more travel per person). Let x be the pass-mi in 1900. Multiply x by 210/340 to eliminate electric railway travel and then divide by 5.5 resulting in 0.112x pass-mi in 1865. This implies that travel by rail in 1865 was only about 11% of that in 1900. Since some of this travel was on trains that burned coal, travel on wood-burning trains in 1865 was likely less than 10% of all rail travel in 1900.
Thus since we now travel 200 times as much as in 1900  , we travel almost 2000 (0.1 x 200) times as much on motorized transport than in 1865.
For 1900, 7.5 pass-mi/gal is based on 4.5 pass-mi/kwh and a generation energy intensity of 6.0 lb-coal/kwh.  with 1 gal. gasoline = 10 pounds coal (in heat value). See 
The 4.5 pass-mi/kwh is a rough estimate, based in part on the figures of 4.87 for 1927 and 4.62 for 1930. These two values are calculated based on the kwh reported by American Transit Association's: "Transit Fact Book", 1948, p.27: "Electric Power", and the passenger-miles reported in [BusFacts-1948]. In 1900, most of the electric railway lines were short and not interurban. Therefore they made more frequent stops than in later years and likely used a little more energy per passenger mile. At the same time, some early streetcars tended to be light and small which would tend to make them more fuel-efficient.
Another estimate of pass-mi/kwh (for the 1970's) is [Chomitz] On p.29 Table 8, one can calculate: PM/kwh = 6.1 (Cleveland), 2.0 (Philadelphia, "Red Arrow") and 1.9 (TNJ, Newark, New Jersey). It's mentioned that the Cleveland line is a "showcase" system and is not typical but that the other two use heavy cars and are likely not typical either. So an average would be about 4 which is not far from the 4.5 used for 1900.
For 1970, 4 PM/kwh is about 44 PM/gal at the power plant heat rates between 1960-2000. This is about double that of the automobile prior to the 1970s (14 mi/gal with 1.7 people). Since many electric railways were interurban, a comparable auto trip would consist of both urban and rural driving and thus overall auto energy-efficiency is used for this comparison.
As a sanity check, the separate edition for 1902 of [Census-1912] p.229 shows an average of 2.14 kwh/car-mi based on 307 selected electric railways. Multiplying this by the assumed 4.5 PM/kwh results in 9.6 passengers per car (on average). Given that streetcars were much smaller in those days, and that the streetcars were apt to be nearly empty when they started from the end of the line near the outskirts of the city, 4.5 PM/kwh seems reasonable.
Sources of "statistics":
1907-1927 [Stat. Abstract 1930]
1950-1970: [Hirst] pp. 14, 37
1970-2000: [TEDB] for "Rail transit"
Only the [Hirst] and [TEDB]report energy-intensity. [BusFacts] only reports Pass-mi which allows calculation of energy-intensity using TransitFacts and the power plant heat rates. It might seem that we have better data for 1925-35 and 1950-2000 but this is not necessarily so as will be explained.
For 1950-2000 the following are reported per above in BTU/Pass-mi
Hirst TEDB 1950 3900 1970 2453 (Note discrepancy for 1970) 1955 3800 1975 2962 1960 3900 1980 3008 1965 3900 1985 3461 1970 4100 1990 3453 1995 3818 2000 3105
Note that for 1970 [Hirst] reports 4100 but [TEDB] reports 2453. This discrepancy indicates that the values shown above may not be very accurate. What is the reason for this discrepancy? Both claim to have used [TransitFacts] as their source of information so there shouldn't be any discrepancy. However in 1970 [TransitFacts] only reported energy use and non Pass-mi (but did report the number of passenger). Thus to use their data to get say Pass-mi/kwh one needs to estimate the average trip length. The discrepancy thus may be due to differences in estimated trip length.
But now, let's look at the New York City subway system (heavy rail). In 1970 about 88% of electricity used on the electric railways was used by heavy rail per [TransitFacts] Table: Trend of Energy Consumption ... and about 75% of this was for the New York City subways per [Chomitz] p.24 (Table 4). Thus about 2/3 of the energy for the electric railways in the U.S. was used for New York City.
For many years an average trip length for New York heavy rail was estimated (erroneously) to be 7 mi. This was used in "Public Transportation, Operational and Financial Status in the Tri-State Region, 1977" Sept. 1979 by the Tri-State Regional Planning Commission, One World Trade Center, New York, NY, p. 15 (Table I: Annual Public Transportation Trips ...), and p. 18 (Table IV: Estimated Passenger Miles Traveled ...).
The method of making this estimation is described in "City and Suburban Travel" Issue 162, 1975, pp 2-5: Passenger-Miles and Passenger-Trips. It's like the so called "gravity" model with all distances being the same. The explanation below has been slightly modified to insure flow conservation. The heavy rail system counts the number of passengers which enter each station at the entrance turnstiles, but doesn't know how far they travel. What percentage of passengers entering a given station (say station A) are headed for say station B? If we can estimate this for all stations then we know the flow of passengers between all pairs of stations and can readily find both passenger-miles and average trip length since we know the distance between all pairs of stations.
But how to estimate the percentage that go from A to B? Well, there's a simple (but erroneous) way to do this. Each station has a known market share which is the percent of total passengers which enter that station in a fixed period of time (say a year). For any station, assign the distribution of destinations to be directly proportional to the market share of each destination station. Let's say station B has 3% of market share. So we might assume that 3% of the people entering all other stations go to station B. This method must be corrected so as to assign all flow since for passengers entering station A, the market shares of all other stations don't add up to 100%. So for station A, just find a correction factor which multiplies the market share of all other stations (other than A) so the adjusted-market-shares of non-A stations add up to 100%. These are just the market shares of the other (non-A) stations if one neglects the existence of station A in calculating them.
But unfortunately, no consideration is given to the fact that in most cases, passengers have a preference for shorter trips so as to save time. Thus, the estimates obtained using the above method are likely to be too large. Such errors are especially relevant to systems such as New York where it takes extra time and effort to transfer from one train to another so as to go a longer distance.
So one hypothesis is that [TEDB] used the above distance estimate (at least for New York) trip length. [Hirst] seems to have used an average trip distance of only 3.5 miles (assuming he considered revenue passengers only). So which estimate is correct? One might expect that the true value is in between the two estimates. But there is still another consideration: the figures for the amount of electric energy used.
For New York heavy rail, it appears that the amount of energy use reported is that of the energy supplied to the traction substations less 10% to account for losses in conversion of AC to DC electricity plus the heating losses in the 3rd rail. This seems to correspond to what is shown in [TransitFacts] considering that about 75% of this figure is for New York City. However the amount of electricity used for non-traction purposes (signals, escalators, ventilation, drainage, lighting, supplying transit offices, etc.) is about 10% of that used to supply the traction substations. Thus the total energy used is roughly 20% higher than reported. It's not clear what portion of this additional energy should be allocated to transportation of passengers. Both the [TEDB] and [Hirst] figures neglect this "overhead" 20% energy.
In view of this, the [Hirst] estimates may be closer to the truth than the [TEDB] estimates. More work on this topic of electric railway energy intensity is needed.
Automobile efficiency also depends on automobile occupancy. The U.S. Federal Highway Administration publishes a "Nationwide Personal Travel Survey" (=NPTS) every 10 years or so. The first (called .. Transportation Study) in 1970 was seriously in error (on the high side) regarding automobile occupancy. Later surveys are also suspect. The 1970 study erroneously reported 1.4 persons/car (average) on trips to work while the U.S. census reported 1.17. Just watching cars pass by on an early weekday morning indicated that the 1.17 figure was the correct one (the author actually did this in the 1970's).
Occupancy data from NPTS for 1977 and 1983 also appear to be in error by a factor of 2. For a comparison of NPTS to census data (but no explanation for the discrepancy) see: 1990 NPTS Travel Mode Special Reports. DOT, Federal Highway Administration, Dec. 1994. Fig. 3: Carpooling and Average Vehicle Occupancy". This figure shows that in 1990 the error disappeared and NPTS agrees with the census.
This error is likely due to taking a simple average of the number of occupants as reported by both drivers and passengers. To get a correct figure of the number of persons per auto, one should only sample the drivers. Even better, one should sample both drivers and passengers but use a weighed average, assigning the weight 1/n to an observer who report n occupants in a car. But this was apparently not done until 1990. Thus the large errors.
For heat values, I've used the high heats of combustion, which were traditionally used in the past: 125,000 BTU/gallon for gasoline. For coal I've used: 12,500 BTU/pound (power generation) 13,100 BTU/pound (railroads). This results in 1 gallon of gasoline being equivalent to: 10 pounds of coal (power generation) or 9.5 pounds of coal (railroads).
For gasoline, this seemingly conflicts with the figure of 114,000 BTU gallon, reported by Chevron. See Fuel Economy of Gasoline Vehicles. But this discrepancy is more apparent than real.
What has happen is that there are two different values of BTU/gallon for the same batch of gasoline. One is the high (or gross) heat of combustion and the other is the low (or net) heat of combustion. The high value is obtained when, after the combustion, the water in the "exhaust" is in liquid form. For the low value, the "exhaust" has all the water in vapor form (steam). Since water vapor gives up heat energy when it changes from vapor to liquid, the high value is larger since it includes the latent heat of vaporization. The difference between the high and low values for gasoline is significant, about 8 or 9 percent. This accounts for most of the apparent decrease in the heat value of gasoline since Chevron is reporting the low heat of combustion. See Appendix B of Transportation Energy Data Book. They give 115.4k BTU/gallon as the low heat value for gasoline.
In "Fuels and Combustion Handbook" Ed. by Allen J Johnson, McGraw-Hill, New York, 1951. p. 364 states that the higher heat value (gross) is the standard ordinarily accepted in the USA. Foreign countries tend to use the lower heat value (net). Would it be better to use the low values? Probably yes, since practical engines exhaust the water as a gas (vapor). The heat values for coal are also given as the high heats of combustion. One uses these heat values to determine how much coal is equivalent (in heat value) to a gallon of gasoline. I've used only the high heat values for both coal and gasoline because it's traditionally done this way.
But one may object to this. Coal is black and mostly carbon. If it were pure carbon, it would not generate any water vapor when burned. This is because a fuel must have hydrogen in it to form water which contains hydrogen (H2O). Thus the heat of combustion for a hypothetical "pure coal" (consisting only of carbon) would have only one heat of combustion. The high (gross) and low (net) values would be the same. So in this case it would be better to use the low heat value of gasoline for calculating a gasoline-to-coal equivalence.
Real coal does contain some hydrogen . But the difference between the high and low heat values is only say 3.5% . See the "Fuels and Combustion Handbook", op cit, p.367. Thus a better comparison would be to use the low heat values for both coal and gasoline. Doing this would make the old coal-based transportation economy of 1900 about 5% less energy-efficient than what I've estimated. But gasoline is a highly refined product as compared to coal, so one could argue that we should increase its BTU value to account for that. This would tend to cancel out the 5% bias mentioned above.
In 1950 the U.S. Bureau of Mines adapted 13,100 BTU/pound for coal but today reports 12,000 to 12,500 BTU/pound. The U.S. Dept. of Energy claims that typical coal today (2000) is only about 12,000 BTU/pound. What was the BTU/pound of coal in the past for railroads and power plants? In footnote 33, p. 184 of [Energy in Am. Economy], it mentions that electric utilities used coal of a lower heat content (12,263 BTU/pound). The 13.1k BTU/pound value is mentioned in this footnote 33 as well as on p. 317 of [Ayres]. Some railroads used anthracite coal which Ayres (p. 317) shows at 12,700 BTU/pound. So I'm assuming that railroads in the past used coal of a higher heat value than power plants.
Comparing the above to [TEDB] for 2000, shows that the energy intensities for the auto is roughly equal to that for urban bus transit but is somewhat higher than intercity rail (Amtrak).
overall auto BTU/PM = 125,000 / (22 x 1.6) = 3,550 intercity auto BTU/PM = 125,000 / (26 x 2.0) = 2,400 <about 33% lower) urban auto BTU/PM = 125,000 / (20 x 1.4) = 4,460 (about 25% higher)
Rail transit is an exception. But the energy data they report to the government doesn't include the energy used for lighting and air conditioning of stations. See National Transit Database Internet Reporting, Resource Module. Compare the 72.8 kBTU/vehicle-mi propulsion energy for rail transit (see p. 2-14, table 2.11 in [TEDB] for 2000) to the BTU/vehicle-mi reported for station energy (see p. 62, table A-3 in [UrbanTransAndEnergy]). It looks like station energy is roughly 10% of propulsion energy. This results in rail transit being 25% more energy-efficient than the auto.
The energy-intensities reported for transit may be too low due to possible overestimation of passenger-miles by the transit operating agencies. See NPTS 1990: "Limitations of Data on Transit". I have made no attempt to correct this since it's not clear how much it is in error. Since many persons using transit would travel alone if they went by auto, a fair comparison might use a load factor (persons/auto) of say 1.3 instead of the 1.4 I used. These two biases are in opposite directions and tend to cancel.
Another consideration when comparing the auto to transit is circuity. By auto, one usually travels by the shortest route, but since transit is not located everywhere, passengers often travel further than if they were to go via auto. This favors the auto by say 20%. However, "autos" above excluded SUVs so factoring in this consideration still favors rail by about 10%.
The British Economist, William S. Jevons in his 1865 book, The Coal Question, pointed out that increasing the efficiency of using coal only leads to more consumption of coal.
More recently, this was called the "rebound effect". Energy Efficiency and the Rebound Effect Does Increasing Efficiency Decrease Demand? - NLECRS Report: RS20981. See also: Khazzoom-Brookes postulate - Wikipedia and rebound effect book
The first article above claims that increasing efficiency does save energy, but not as much as one would expect due to stimulation of demand. When energy-efficiency is increased there is the price effect and the income effect and both effects tend to increase energy consumption.
The saving of energy due to increased efficiency may lead to a decrease in the price of fuel, due to a decreased demand for it due to the higher efficiency of its use. The decreased price in turn tends to increase to consumption of that fuel. This is the price effect.
Also, since consumers save money due to the increased energy efficiency, they have additional money to spend on things that consume lots of energy (or took energy to manufacture). They might buy a SUV, go on an airplane trip, buy a hot-tub or a high-powered computer, etc. This is the income effect. Due to the savings from energy efficiency, consumers in effect have more disposable income to spend on energy.
Realistically, these effects may not be very pronounced. If a fuel is becoming more scarce as it is depleted, or if demand for it is growing for situations where the energy-efficiency measures were not applicable, then there may be little (if any) decrease in its price. If it costs significantly more to build energy efficiency into a product and the consumer must pay this cost, then the income effect could be minor (or even the opposite of what was described above).
But there are other circumstances that stimulate energy consumption. One is the income effect of technological "progress" resulting in higher productivity which means that people have more money to spend on energy. Another is technological and societal change which creates new "needs" which consume energy. For example, the invention of the railroad and automobile resulted in the creation of new travel needs which was set in concrete and steel by locating places of residence, employment and shopping such that a lot of travel is needed to travel to and from them.
One way to counter the factors simulating the consumption of energy is to place a high tax on it, or even more restrictive, rationing. But whether or not either of these two measures should be done and just how they should be done is beyond the scope of this article.
The thesis of Jevons has been insidiously used by those who seem to oppose energy conservation. The book "Why Energy Conservation Fails" by Herbert Inhaber only presents one side of the question and is thus biased. Yet many of the points he makes are correct. What's wrong with this book is what was omitted from it, such as suggestions for reducing demand by taxes and concern about future generations, etc. Another article by Herbert Inhaber et. al. appeared in "The Sciences" v.34 #6, Nov-Dec. 1994: Road to Nowhere (Energy conservation often backfires and leads to increased consumption).
Another article about Jevons paradox is by H. Herring: "Is Energy Efficiency Environmentally Friendly?" is found in Energy & Environment, Volume 11, Number 3, May 2000, pp. 13-325.
Note that in the late 1980s, the fuel economy of new cars peaked and started to slightly decline thereafter. Nevertheless, energy efficiency of cars on the road continued to increase in the late 1980s and throughout the 1990s due to the fact that most new cars were still more efficient than the older ones that were being junked.
For 1940, Transit Fact Book says that no fuel data is available for Urban Buses. Thus estimates for 1920-1940 are missing. Compare the figures below with Lawyer's 4460 BTU/Pass-Mi estimate for the urban auto, and 2400 for the intercity auto (both for 1990). See 
Sources of "Statistics":
Bus Energy Intensity in BTU/Pass-Mi -Intercity- ------Urban------- Year Hirst TEDB Hirst TEDB Lawyer 1945 2650 1950 640e 3100 1955 1100e 3400 1960 1500 3400 1965 1600 3500 1970 1600 1674 3700 2472 (note urban discrepancy) 1975 988 2814 1980 1082 2813 1985 964 3423 1990 962 (2400*) 3794 (4460*) * for autos per Lawyer 1995 964 4310 2000 932 4515
From 1975-2000 [TEDB] shows that the energy-intensity ranges from 932 to 1286 BTU/PM. There seems to be no clear trend. 1000 BTU/PM would be equivalent to 125 PM/gal of gasoline. The bus companies brag (on the Internet) about their energy-efficiency and quote figures in terms of diesel fuel, which results in a PM/gal about 10% higher than it would be in terms of gasoline (due to the larger heat content of diesel fuel per gallon).
The American Bus Association, claimed 160 PM/gal for 1999. See BUS TOUR BASICS - New Mexico Arts (This claim was previously at the now boken link: "http:www.buses.org/files/download/0716ABA.pdf"; original source : ABA - Industry Facts).
But reducing this 160 PM/gal-diesel to per gallon of gasoline gives about 145 PM/gal. Now a large number of the members of this association are charter bus operators. Charter buses would seem to be more likely to be nearly full than scheduled intercity buses and thus get higher PM/gal. So if we think of intercity buses as including charter buses, then the energy-efficiency is higher. But if we consider only scheduled buses available to the public, then the energy-efficiency might be about 130 PM/gal.
The [Hirst] estimates cite ATA (American Transit Association) as a source. But the ATA's [TransitFacts] doesn't give pass-mi but only shows the number of passengers. Contacts with them reveal that they did not collect Pass-mi data then. However, the number of passengers is reported and Hirst seems to have multiplied this by an assumed 2.5 to 2.6 miles average trip length to obtain his results (assuming he used unlinked trips or total pass-mi). In 2000 APTA (new name of old ATA) p. 75 of 2002 "Fact Book" reports 3.7 miles for average unlinked bus trip length (no transfers).
But urban bus trips have become longer. One reason is that transit agencies often took over long Greyhound (etc.) commute bus routes which were previously considered to be "intercity" but are now classified as "urban". In some cases, the construction of Freeways (and availability of subsidy) led to establishing long bus routes on freeway. Urban sprawl contributed to longer trips. So it Hirst's estimate of about 2.6 miles for the 1950-1970 period may be reasonable, especially for the 1950s.
However Hirst assumed 136,000 BTU/gallon for bus fuel. But [TransitFacts] shows that prior to 1958, bus fuel was mostly gasoline which has 125,000 BTU/gallon. For 1950, about 4 times as much gasoline was used as diesel (at 137.5 BTU/gal) so the average was about 127,000 BTU/gal (and not 136,000 as used by Hirst). This makes the Hirst energy-intensities several percent too high for the 1950s but only a few percent too high for the 1960s as gasoline buses were being phased out. But making a correction for this error fails to eliminate most of the discrepancy.
So what explains the discrepancy for 1970: Hirst: 3700 BTU/Pass-mi TEDB: 2472 BTU/Pass-mi. Even though Hirst's work only goes to 1970 an extrapolation of it indicates that this discrepancy continues well after 1970. When the government began to collect estimates and data from mass transit agencies in the early 1970's what they sometimes got (based on my observations at that time) were estimates which were often biased to make the Pass-mi too high. As time went by, the government began to "require" more accurate estimates. Although this was likely not very well enforced, it did apparently result in better estimates since the reported energy-intensity has continued to increase since 1970. Thus the increase may be partly due to better estimates. The poor energy-intensity is partly due to poor ridership and also to subsidy which permits operations to continue with poor ridership.
See Ekonomicheskie Problemy Razvitiya Transporta (in Russian, translated title: Economic Problems of Transport Development), editor: A. A. Mitaishvili. Moskva, Transport (publisher), 1982. See table 7.2 (on modal shares) p. 78.
See "Panorama of Transport" (an annual) by Eurostat (of the European Commission, part of the European Union, EU). Luxembourg, 2003. A figure on p. 33 shows automobilisation (or motorisation) for both Western Europe and the U.S. On pp. 69-70 the modal spilt (in pass-km) is shown for 1970-1999.
A major source of data in English is:
EDMC Handbook of Energy & Economic Statistics in Japan by The Energy Data and Modelling Center, The Institute of Energy Economics, Japan and published by The Energy Conservation Center, Tokyo, Japan. The 2001 edition was used for this section: p. 110 (Volume of Transportation by Mode), p. 112 (Energy Intensity by Mode)
Billion Passenger-kilometers Year Auto Bus Rail Air Truck Sea Total 1965 62 80 235 3 11 3 416 1970 277 103 289 9 19 5 703 1975 329 111 324 19 16 7 804 1980 414 110 315 29 16 6 891 1985 511 105 330 33 16 6 1000 1990 727 110 385 52 16 6 1296 1995 806 97 400 65 14 6 1388 1999 858 88 385 79 12 5 1428
In the table below, the second Rail figure (designated by x3) is just the first one multiplied by 3 to account for the fuel needed to generate electricity for electric railroads. The first "Rail" figure is the one reported from Japan. The EDMC data source from Japan notes in the "Explanatory Notes" that the efficiency of electric power plants was taken into account for the "Energy Balance Table" but doesn't mention the transportation Energy-Intensity Table which implies that it fails to take into account power plant efficiency. The fact that the "Final Energy Consumption by Source" on p.39 fails to account for power plant efficiency, tends to imply that the transportation Energy-Intensity table (p. 112 in the 2001 edition) didn't do it either.
kcal/passenger-kilometer x3 (see above) Year Auto Bus Rail Rail Air Truck Sea 1965 561 113 57 * 1507 1354 191 1970 373 116 48 144 1026 1012 220 1975 518 129 45 135 870 1343 203 1980 544 122 48 144 795 1151 214 1985 518 125 46 148 705 1341 174 1990 488 145 48 144 550 1528 202 1995 560 155 49 147 569 1257 253 1999 584 165 51 153 441 1854 488
* For 1965 I've assumed that a significant part of the energy came from diesel trains. Thus multiplying by 3 is not valid. This table and the previous table of modal shares implies that from 1965 to 1999, the average reported energy intensity for all modes combined, steadily increased from 190 kcal/pass-km to 417 kcal/pass-km. However this reported value is in error due to neglect of the losses in generating electricity for electric trains. So the actual increase in overall (all modes) energy intensity is not quite as great as the 190 to 417 kcal/pass-km implies since the 190 figure is likely much too low.