TRANSPORTATION, EVOLUTION OF ENERGY USE AND

Transportation is energy in motion. Transportation, in a fundamental sense, is the application of energy to move goods and people over geographic distances. Freight transportation may be regarded as part of complex logistical and/or distribution systems that carry needed materials to production facilities and finished goods to customers. Transportation of passengers can serve long-distance travelers, daily commuters, and vacationers, among others. Special systems accommodate the requirements people have for mobility throughout the day. A wide variety of specific technologies and management systems are involved, and from the mid-nineteenth century, a large portion of the world's energy supply has been devoted to transportation.

When sailing vessels predominated at sea and when horses or draft animals provided basic land transport, energy demands by transport systems were small. With the advent of increasingly reliable steam power for river, lake, and ocean vessels beginning in the late 1820s, together with the spread in the 1830s of steam railways running long distances in Europe and North America, demand rose sharply in the industrialized countries for wood and coal as fuel. Coal became the fuel of choice for ocean transport as steam gradually displaced sail from the mid-to the late nineteenth century, since far more Btus per volume of fuel could be stored in the limited space of fuel bunkers.

Nearly all locomotives in Britain, and many on the Continent, used coal as well. In North America, wood—because of its plentiful supply—was the principal fuel for locomotives and for western and southern riverboats through the late 1860s. Locomotives of some railroads in Pennsylvania burned anthracite—"hard" coal. Most of the earliest coal production in the United States, starting in the 1820s, was anthracite, which was slow-burning but produced very little smoke. That virtue made anthracite the preferred type of coal for home heating and for industries within large urban centers such as Philadelphia and New York, to which the costs of transporting wood were higher than to smaller cities and towns closer to their wood supplies.

Railway use of wood as fuel in the United States peaked at almost 3.8 million cords per year in the 1860s and fell slowly thereafter. From the 1850s, the use of coal—preponderantly the more common type, called bituminous or "soft" coal—increased on railways and on waterways, especially in the East and Midwest as coal production in those regions accelerated. (A ton of good bituminous equaled the heating value of 1¾ to 2 cords of seasoned hardwood.) Two major factors influenced the broad conversion to coal: First, as the quantity mined increased, prices fell—from $3.00 per ton in the 1850s to about $1.00 per ton to high-volume purchasers just ten years later. Second, the country's voracious appetite for wood—for domestic and industrial fuel, for charcoal used in ironmaking, and for construction—had denuded vast stretches of the eastern forests by 1880. In that year U.S. railroads consumed 9.5 million tons of coal, which accounted for about 90 percent of their fuel supply.

Electricity, generated primarily from coal, became widely used for transport within and near cities, as trolleycar systems proliferated after the late 1880s. The enabling developments were, first, successful forms of large-scale electric generation from steam-driven dynamos and, second, a practical method of electricity distribution to the railcars. Most such cars took their power from an overhead wire, with electrical grounding through the track. In many parts of the world, trolley systems became a fixture of urban transportation in large and medium-size cities. Trolley companies usually owned their own power-generation stations and often provided a given city with its first electrical distribution network. Trolley companies were therefore eager to sell electricity and often sponsored efforts to spread the use of electric lighting systems and other electric appliances. Elevated urban railways, powered at first by tiny, coal-fired steam locomotives in the 1880s and converted later to electricity, also helped ease urban congestion in New York and Chicago. A related development by 1900 in a few of the world's major cities was the electric-powered subway.

Especially in North America, a direct effect of the electric trolley—from about 1890 through the 1920s—was the rapid growth of suburbs. In some cases, trolley systems that extended beyond city boundaries accelerated the expansion of existing suburbs. In many other cases, new suburbs sprang up, facilitated by the cheap mobility offered by newly built trolley lines. Long-distance, electric interurban rail systems also grew at a fast rate in the United States after 1890. Throughout New England, the East, and the Midwest, and in many places in the South and West, travelers and longer-distance commuters could use electric railcars connecting small towns with medium-size and large cities, over distances of up to a hundred miles or so.

Since the mid-twentieth century, petroleum has been the predominant fuel stock for energy used in transportation on land, water, and in the air. The shift began slowly. Oil-fired boilers for ships were tried in the 1860s. A railway in Russia fired more than a hundred of its steam locomotives on oil in the 1880s. By the first decade of the twentieth century—and although coal was still the favored fuel for steam transportation throughout the world—several thousand steam locomotives in the western part of the United States as well as a few ocean vessels were fired by residual oil from a rapidly growing number of refineries or, in some cases, by light petroleum.

Regional scarcities of coal initially drove these uses. As petroleum became more abundant and as its price fell, oil became more attractive. In firing boilers, fuel oil possessed only a slight advantage over good-quality coal in Btus per unit volume. But liquid fuels were much easier to handle and store than coal. Competitive pressures kept the prices per Btu of residual oil and coal quite close.

The transition to oil for the boilers of oceangoing steamships was well along by the 1920s. A coincidental development in the early part of the century was the steam-turbine engine for ships, which mostly displaced multicylindered steam piston engines in marine applications; the turbine is more energy-efficient at constant speeds maintained over long periods of time. A decreasing number of older riverboats, towboats, lake boats, and freighters continued to use coal through the 1950s (and a rare few such steam vessels were still in use in the 1980s). As late as 1957, U.S. railroads purchased $48 million worth of bituminous coal for steam locomotive fuel—and $374 million of diesel fuel. By 1960, all use of steam locomotives on major lines in the United States and Canada had ended, and by 1970 the change to diesel locomotives was virtually complete worldwide, except in some parts of China, India, Africa, and Eastern Europe. Thus the use of coal as a transport fuel ended for the most part in the late twentieth century, except for electricity (generated from coal) used on a small percentage of the world's railway mileage.

The burgeoning growth in the use of petroleumbased fuels in transportation came with the widespread use of automobiles and trucks after 1910 and the beginning of air travel after World War I. In the 1890s, little gasoline was consumed. It was regarded as an explosively dangerous by-product of the refining process in the production of kerosene (a petroleum distillate) for lighting. But with the invention of practical automobiles in the 1890s in the United States and Europe, demand slowly grew for a high-energy fuel that could be used readily in small, internal-combustion engines. In such use, the high Btu per unit volume of gasoline was a distinct advantage. The story of the huge oil companies and gasoline distribution systems that arose in the United States and overseas in the early twentieth century is one driven entirely by the rise of the automobile.

During the first two decades of the twentieth century, several hundred firms in Britain attempted automotive production, and nearly 3,000 tried to do so in the United States. But there was one car that created much of the rising demand for gasoline: the Ford Model T. Between 1908 and 1927, 15 million Model Ts rolled out. Ford built half of the automobiles manufactured in the world in 1920. The Model T's low price and high reliability created a vast pool of willing purchasers. A result was to sweep away the economic incentives that might have supported a viable market for alternative fuels or motors for automobiles, such as electric or steam propulsion. Versus the electric, a gasoline engine provided much greater operating range; versus steam (such as the compact boiler and engine used in the temporarily popular Stanley steamer), a gasoline engine was much simpler and less expensive.

After 1910, gasoline-powered trucks became common. Their utility eventually replaced horse-drawn vehicles in farm-to-market and intracity use, though that replacement took decades. Even in the industrial world, horses provided a large but declining share of intracity freight transport through at least the 1930s and early 1940s. Highway buses became popular in the 1920s. Such buses quickly displaced the long-distance, electric interurban rail systems of the 1890s and early 1900s.

Rudolph Diesel first patented his engine in 1892, but it was not until 1910 that a successful application was made in a vessel. The first diesel engines suitable for use in trucks came in the early 1920s. Annual U.S. production of diesels did not exceed one million horsepower until 1935. Over the next two years that production doubled, largely because of railroad locomotive applications. Due to the high compression pressures a diesel engine must withstand in its cylinders, it must be built heavier than a gasoline engine of similar output. But the diesel's advantage is that it is the most energy-efficient internal-combustion engine yet developed. Marine diesel design advanced in the 1930s and during World War II, leading to greater use in larger transport vessels from the late 1940s. The demand for high-quality diesel fuel—similar to kerosene—thus expanded.

With the inception of the U.S. interstate highway system in the late 1950s, the modern long-distance highway tractor and its semitrailer evolved and became the predominant method of freight transportation for time-sensitive, high-value goods. Elsewhere in the world, different forms of the long-distance truck took over most freight transport. Today, in the United States and elsewhere, these trucks are almost universally diesel. In the United States in the 1990s, some 39 percent of intercity ton-miles of commercial freight were borne by rail, 28 percent by trucks, and 15 percent on lakes, rivers, and canals (the rest was carried by pipelines and a fraction of 1% by air). Diesel fuel powered nearly all this road, rail, and water transport.

An aspect of transportation that has a heavy bearing on energy consumption is horsepower. Transport can be measured in units of work—tons hauled per mile, for example—but energy consumption is more proportionately related to power, such as tons per mile per unit of time. For a given load carried over a given distance, higher speed requires more power and hence more energy. Thus there is a trade-off especially important in all forms of transportation: Fuel-saving strategies often involve reduced speeds, while increased transport capacities of systems per unit of time often necessitate higher speeds and therefore require higher fuel use per ton-mile or per seat-mile.

Aviation has been powered from its beginnings by gasoline. Only spark-ignited gasoline engines proved able to provide the extremely high power-to-weight ratios needed by aircraft engines, where weight is always at a premium. During World War II, German and British engineers developed the gas-turbine engine for aircraft (known commonly as the jet engine). Such engines ran best on a variation of kerosene. In the "turbojet" form of the gas-turbine, there is no propeller; in the "turboprop" form, the central turbine shaft of the engine turns a propeller through a gearcase.

In transport applications in the 1950s, the jet's favorable power-to-weight ratio and efficiency at high altitudes resulted in a travel revolution. (The first commercial jet, the de Havilland Comet, first flew with paying passengers in 1952; the pioneering Boeing 707 came a few years later.) Speed was only one factor. Flying at more than 30,000 feet—well above the turbulent weather systems ordinarily encountered by piston-engined aircraft, which operate most efficiently up to about 20,000 feet or below—the comfort level of jets allowed millions of people to accept these new planes as long-distance transport.

Turboprop types of aircraft proved more reliable and cheaper to operate than piston-engined airplanes for short hauls and more fuel-efficient than turbojets in such use. Overall airline patronage shot up dramatically after 1960. Since the 1980s, air express has boomed as well. Thus most aviation fuel used today is well-distilled kerosene, with a small portion of antifreeze for the extremely low ambient temperatures at high altitude. High-octane gasoline powers much of the "general aviation" sector of private aircraft, where piston engines are still the norm for planes of up to four or five passengers.

During the oil shortages of the 1970s and early 1980s, researchers in the United States and Europe investigated alternative fuels for transportation. Shale oil deposits were tapped, and other projects experimented with the conversion of various grades of coal to oil (a technology developed by Germany in World War II). Two U.S. railroads (the Burlington Northern and the Chessie System) seriously considered a newtechnology steam locomotive that would burn coal in a gasification furnace, thus controlling emissions. Meanwhile, diesel manufacturers experimented with modified engines burning blends of finely pulverized coal mixed in fuel oil. While these engines ran reasonably well, tiny amounts of noncarbon impurities in the pulverized coal inevitably built up within the engines' cylinders, causing rough running or damage. Stabilizing oil prices from 1982 through 1999 removed most incentives for further research.

From 1980 to 1998, total U.S. petroleum consumption ranged between 15 million and 19 million barrels daily, with consumption at the end of the 1990s about the same as in the peak of 1978. Use of petroleum for U.S. transportation was slightly less than 10 million barrels per day in 1980 and was about 12 million barrels in 1997, or some 60 percent of total domestic oil consumption. That oil consumption rate supported a growth in U.S. freight of about 20 percent from 1980 to the late 1990s, amounting in 1997 to a bit less than 15,000 ton-miles of freight transported per person per year.

Travel has also multiplied. The U.S. Departments of Commerce and Transportation surveyed long-distance trips in 1977 and 1995 (with a long-distance trip defined as a round-trip of at least a hundred miles each way). Between those years, long-distance trips per person per year by automobile grew by almost 90 percent; by air, such trips nearly trebled. Increased mobility is a central feature of modern life.

All modes of transport—by road, rail, water, and air—have increased engine fuel efficiency and have instituted other fuel-saving strategies since the oil shortages of the 1970s. New turbine-engine aircraft have doubled the average fuel efficiency of earlier jets. On railroads, a gallon of diesel fuel moved 235 ton-miles of freight in 1980; in the early 1990s, a gallon moved more than 360 ton-miles. Average automobile fuel mileages have improved. Redesigned hull shapes and large, higher-efficiency diesel engines have lowered fuel costs in maritime transport.

New vehicles, propulsion systems, and fuels are on the horizon: "hybrid" automobiles (combining an electric motor, batteries, and a gasoline or diesel engine), better electric cars, greater use of compressed natural gas (CNG) and propane for urban fleet vehicles such as taxis and delivery trucks, fuel cells (using gasoline, natural gas, or propane as the feedstock for hydrogen), methanol or ethanol to supplement gasoline, and other technologies are advancing. For such technologies and fuels successfully to compete with oil in the transportation market, the techniques to liquefy and compress natural gas would need to become cheaper, new types of storage batteries must be made practical, and the necessary infrastructure to support CNG-, fuel-cell-, and electric-powered cars and trucks would need to be developed. The huge worldwide investment in petroleum extraction, refining, and distribution makes economic change in fuel technologies difficult.

In Europe, Japan, and the United States, newer high-speed electric railroad trains are being advanced. Japan has shelved its development since the 1980s of magnetic-levitation trains, but German firms continue work on such systems for possible application in Germany (a "maglev" line has been planned between Berlin and Hamburg) and elsewhere. Engine development for aircraft has recently cut the number of turbojet engines required for a long-distance, high-capacity transport airplane from three or four to two, cutting fuel consumption per seat-mile, and further fuel efficiency increases can be expected in the years ahead.

William L. Withuhn

See also: Aircraft; Air Travel; Automobile Performance; Aviation Fuel; Diesel, Rudolph; Diesel Cycle Engines; Diesel Fuel; Electric Motor Systems; Fossil Fuels; Freight Movement; Fuel Cell Vehicles; Gasoline and Additives; Gasoline Engines; Hybrid Vehicles; Kerosene; Locomotive Technology; Magnetic Levitation; Mass Transit; Methanol; Petroleum Consumption; Propellers; Railway Passenger Service; Ships; Steam Engines; Tires; Traffic Flow Management.

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