Trains and Railroads
Trains and Railroads
Trains are the series of connected railroad cars that are pushed or pulled by one or more locomotives. Railroads are the systems of locomotives, passenger and freight cars, land, buildings, and equipment used to transport goods and customers throughout an area with the use of pairs of parallel metal rails. Railroads have been built and currently operate extensively around the world, on every continent except Antarctica. In August 2005, the Qingzang railroad became the highest line operating in the world when it began operations through the Tanggula Mountain Pass at a maximum elevation of 16,640 ft (5,072 m).
Trains were developed during the Industrial Revolution (which began in England in the eighteenth century) and were arguably that period’s most important product. In many ways, railroads made the Industrial Revolution possible. Factories could not run without a constant supply of raw materials, or without a method of moving goods to market. More than anything, the progress of the railroads depended on the development of motive power, which was, in turn, being driven by technology. If the story of the Industrial Revolution is the story of the railroads, then, the story of the railroads is the story of technology.
Like so much else in western culture, railroads had their roots in ancient Greece. Farmers and merchants transporting goods realized that their wagons could travel more quickly on a smooth, hard surface with its reduced friction than on soft dirt roads. Where possible, they cut ruts into the rock to guide the wagon
wheels. These rutways were limited to areas where the rock was near the surface, but the efficiency of the approach was demonstrated.
The rutway technology was submerged in the full-width Roman roads and lost in the eventual fall of the empire. In the late Middle Ages, however, a variation of the idea surfaced. In sixteenth and seventeenth century Germany and England, primitive railway systems were developed in which wood-wheeled carts ran on wooden rails. These early lines were developed primarily for heavy industry such as coalmining, to make large volume transport viable. The ascents were made using horsepower and the descents were made with the benefit of gravity and brakes. The reduced friction of the wagonways allowed horses to haul several times the load they could manage on a normal road, and the rails guided the wagons along.
These wooden rail systems had a number of disadvantages. When wet they were extremely slippery, causing the carts to slide out of control on grades. They were not particularly strong or durable. In particular, carts with iron wheels quickly wore out the soft wooden tracks. In 1767, Richard Reynolds of Coalbrookdale, England, fabricated the first iron rails. The metal rails reduced the rolling friction of the wheels while lasting longer than the wooden alternatives. The way was clear for motive power.
In its simplest form, a steam locomotive consists of a firebox, a boiler, a cylinder or cylinders, and wheels, all of which are mounted on a rigid frame. The flames in the firebox heatwater in the boiler to create steam. The steam is directed into a cylinder where its force is used to push a plunger attached by a connector rod or gears to the driving wheel of the engine. These connecting elements force the wheels to turn, which moves the engine along the track.
Wheels are classified as drive wheels, which provide motive power, and carrying wheels, which distribute the weight of the engine and add stability. Carrying wheels are further divided into leading wheels; i.e., those ahead of the drivers, and trailing wheels, or those behind the drivers. A common classification scheme for steam locomotives gives the number of leading wheels, the number of driving wheels, and the number of trailing wheels. The locomotive-style engines of the American West, for instance, would be classified as a 4-4-0: four leading wheels, four drivers, and no trailing wheels.
The first self-propelled steam vehicle was built by Frenchman Nicolas-Joseph Cugnot (1725–1804) in 1769, followed by Scottish engineer and inventor William Murdoch’s (1754–1839) model experimental locomotive in 1784. In 1802, British engineer and inventor Richard Trevithick (1771–1833) built the first full-size locomotive to run on rails, thus winning a wager for his employer. A horizontal cylinder sat in the boiler and drove a piston, which drove a connecting rod that connected to a crank/flywheel. A set of gears transferred energy from the crankshaft to the drive wheels that moved the engine. To meet the terms of the bet, the locomotive successfully pulled a series of cars loaded with ten tons of iron and 70 people.
Trevithick used an artificial draft through the firebox to fan the flames of the coals, an important innovation. This increased the heat of the fire, generating larger amounts of high pressure steam. He dispensed with any additional traction mechanism to keep the engine from slipping, convinced that the friction between the iron rails and the wheels was enough to drive the vehicle forward. His invention worked admirably. At several tons in weight, however, it was far too heavy for the brittle iron plateway and left a string of broken rails in its wake.
Traction, or wheel-to-rail adhesion, is fundamental to the operation of a locomotive. In order to move a string of cars, the locomotive drive wheels must grip the track. If traction is insufficient, the wheels simply spin without pulling the train forward, just as car wheels can spin uselessly in mud or on ice. This was a special concern for early locomotive designers who, unlike Trevithick, were not convinced that wheel-to-rail adhesion was sufficient to move the train down the track. Because frictional force between wheels and rail is proportional to the downward force or weight on the driving wheels, lighter engines were more likely to encounter adhesion problems. Heavier engines had better adhesion but their weight tended to break or split the brittle cast iron tracks, and locomotive builders were under continual pressure to reduce engine weight.
A variety of solutions that balanced the issues were proposed and built. In 1812, British mining engineer and inventor John Blenkinsop (1783–1831) built a substantially lighter engine than Trevithick’s, compensating for any loss of adhesion by using a rack and pinion drive. The drive wheels were cogged and rails were toothed on the outside face. The teeth on the drive wheels meshed with the teeth on the rails, driving the locomotive forward with no chance for slippage. Costly and complicated, the rack and pinion drive soon proved to be unnecessary for conventional railroads and never became popular. Other high traction methods such as chain drive or external pushing legs were simply impractical, and most of the locomotives that followed reverted to adhesion drive.
A second Blenkinsop innovation became a standard feature of almost all subsequent steam locomotives. Blenkinsop designed a two-cylinder engine, with a cylinder to power the drive wheel on each side. This eliminated the use of an overhead flywheel to transfer mechanical energy from the cylinder to the drive wheels. Unlike Trevithick’s design, however, the cylinders on Blenkinsop’s engine were vertical. At high speeds, the rapid bounce of the pistons added a great deal of chop to the engine movement, exacerbated by the fact that the engine had no springs to absorb the motion. Given the weight of the engines, the chop placed a significant amount of stress on the rails, resulting in more splits and fractures.
The next groundbreaking design was an adhesion drive, two cylinder locomotive called the Puffing Billy. It was the first steam locomotive to feature cylinders outside of the boiler where they were easily accessible. Designed by British engineer William Hedley (1773–1843), the Puffing Billy distributed its weight over eight drive wheels, putting less concentrated load on the track and causing less wear.
One of the major locomotive companies during the nineteenth centuries was run by the father-son team of George and Robert Stephenson. The Stephensons were responsible for some of the most important technical innovations in locomotive operation. George Stephenson replaced the cylinder-to-wheel gear interface by coupling and connecting rods, streamlining the design and bringing it closer to the modern style of locomotive. He also introduced the locomotive steam spring, which cushioned the action of the engine. The spring consisted of a vertical, cylinder with a piston that carried the engine weight. Steam forced the piston to the upper end of the cylinder, applying upward force to counter the downward force of the weight of the engine. As a result of the shock-absorbing effect of the spring, the heavy engine rode more easily on its wheels and caused fewer cracks in the iron rails.
Locomotive wheels also cracked frequently, requiring costly replacements and engine down-time. English civil engineer Robert Stephenson (1803–1859) and British mechanical engineer Timothy Hackworth (1786–1850) replaced the solid cast-iron wheels of early engines with a combination design that featured durable, replaceable wrought-iron tires mounted on cast-iron hubs. In his 1827 locomotive the Rocket, Robert Stephenson also introduced the multitube boiler. Frenchman Marc Seguin developed a similar design at around the same time. In the multitube boiler, hot gases from the firebox move through tubes that run the length of the boiler. Heat is exchanged over a much greater surface area, making the design far more efficient than the single chamber type. Around this same time, locomotive designers abandoned the vertical cylinder for the smoother horizontally mounted type, though the cylinders on the Rocket compromised with a slanted orientation.
Steam locomotives were introduced in the United States in 1829. British builders initially supplied them, but the development of American locomotives moved in a different direction from British and European locomotives almost immediately. Britain was a prosperous, settled country and British tracks were sturdy and well-built, with flat roadbeds and low grades. The Americans, on the other hand, were still pushing the frontier west across a vast landscape. Railroad companies were minimally financed, while striving to web the country with rails. Consequently, American tracks were built hastily, with minimal roadbed preparation. Often they consisted of just flat-topped rails spiked onto rough-cut ties. Curves were tighter, grades were steeper, and because the roadbeds were poorly graded if at all, the tracks were uneven. The high performance British locomotives with their fixed, four-wheel suspension did not fare well on U.S. tracks, derailing and breaking axles on the twisting, uneven rails.
The Experiment, a 4-2-0 engine built by American civil engineer John Bloomfield Jervis (1795–1885) in 1831, was the first locomotive designed specifically for use on the American railroads. To modify the British fixed-wheel suspension, Jervis added a four-wheeled truck mounted on a center pivot to the front of the Experiment. Like the front wheels of a car, this truck could shift and turn with the track, compensating for sharp curves and unevenness. The two drive wheels were at the back of the engine, and the Experiment also boasted the novelty of an enclosed cab.
The design was a success and notion of a leading four-wheel truck was widely adopted in the United States. In 1836, Henry R. Campbell patented the 4-4-0 locomotive. Robust and economical, locomotives of this design could soon be ordered from a number of manufacturers. A cowcatcher was added to sweep away livestock from tracks running through open prairie, and a spark-suppressing smokestack kept glowing cinders from flying out to start fires. With these addition, the United States had the American Standard, a rugged, powerful locomotive that was ubiquitous in the nineteenth century United States.
Additional accoutrements were added to these engines. American locomotive manufacturer Matthias Baldwin (1795–1866) was the first to equip a locomotive with warning bells, and American railroad engineer George Washington Whistler (1800–1849) added the first steam whistle. Night travel was at first accomplished by maintaining a fire on a small car hooked to the front of the engine, but was soon superceded by a headlamp.
Meanwhile, the focus in Britain was on speed. Whereas the average speed of the American Standard was around 25 mph (40 km/h), British engines were routinely clocking speeds of 60 mph (97 km/h) as early as 1860. The tracks were flat and smooth with few curves and low grades, and the swift engines were designed with compact, rigid frames and enormous driving wheels. In 1832, Robert Stephenson built the Patentee, a 2-2-0 engine whose design was to dominate in Britain and Europe for many years to come.
Further improvements in steam locomotive technology led to increases in speed and power. To maximize efficiency, double cylinders were constructed in which the steam from the first cylinder was let into a second cylinder to completely exhaust its pushing capabilities. More complete combustion was achieved by installing a firebrick arch in the firebox that routed air around prior to introducing it to the boiler. To improve power, multiwheel behemoths were built. Locomotives with six and eight wheels were commissioned, as well as the less common 10–12 wheelers.
Superheated steam was another method of increasing efficiency. In most early locomotives, steam included a significant portion of what was merely hot water. It was unable to do useful work and took up space in the cylinder where steam could normally expand to do useful work. To address this issue, engineers in Germany and Belgium developed the method of superheated steam. Steam headed toward the cylinders was heated a second time to dry it out, minimizing liquid water content. In tandem with improved cylinder valve gearing, the use of superheated steam increased engine efficiency so much that compound cylinders were eventually phased out as unnecessary.
Steam locomotives reached their peak in the middle of the twentieth century. 4-8-4s and 4-6-4s capable of speeds as high as 95 mph (153 km/h) were built in the mid-1940s, when rail travel dominated overland passenger travel. Even as these streamliners were capturing the imagination of the public, however, diesel and electric locomotives were beginning to take over rail transportation. By the mid-1950s, the numbers of steam locomotives were dwindling rapidly, and today they exist only as sentimental reminders of a bygone era.
Diesel engines are internal combustion engines in which fuel oil is injected directly into the cylinder head and ignited by pressure. They power the wheels by direct gearing rather than the connecting rods of the steam locomotive, providing continual power. Railway diesels have been designed with electric, hydraulic, mechanical, and pneumatic transmissions; today the diesel-electric engine is most common.
When they were introduced early in the twentieth century, diesels offered unprecedented efficiency and performance over steam locomotives. Diesel engines could be operated round the clock, without timeouts to take on water for the boiler or clean out ashes from the firebox. They could carry enough fuel for a day or two of continuous operation, and running them was almost absurdly simple. Crews for the first diesel locomotive in the United States, for example, were trained to operate it in just 15 minutes. Initial capital outlay was high, but operating costs were only a fraction of the cost of steam locomotives.
Electric trains are the other major type of motive rail power. Particularly in Europe, passenger traffic is dominated by electric power.
Electric trains run on both direct and alternating current, with voltage in the 50–100 kV range. The choice of current type is driven as much by economics as by performance, involving as it does a tradeoff of cost and efficiency. Alternating current (AC) offers an economical current supply at the expense of motor complexity. Motors for the more expensive direct current (DC) supplies are very simple. Current is fed to the motors from overhead wires, as with trolleys, or from an electrified third rail along the ground, commonly seen in subways.
from the beginning of railroad development, British and European line surveyors were extremely careful to lay flat, even track, along with minimizing curves and grades. A track set down by George Stephenson, for instance, was laid on stone blocks with very compact foundations. By contrast, most early American tracks were laid hastily on wooden ties. The flimsy rails were easily deformed by the repeated weight of trains, sagging where not supported by the ties. Eventually the ends of the rails would rise up due to this sagging action. When they rose high enough, these so-called snake heads would be pushed up in front of the wheels and either derail the train or punch through the floorboards, impaling those unlucky enough to be sitting above them. To avoid this, American railroads began placing the ties very close to one another, a practice still followed today.
The early wood rails were followed by brittle cast-iron rails. It was only later that more ductile wrought iron was used. Steel rail came into play in the 1870s, as a byproduct of the Bessemer process, a method for economical mass production of steel. The steel rail was more durable, capable of supporting harder wheels and heavier loads. In recent years, rails have become heavier, weighing as much as 100 lb (45 kg) per yard. Much of it is continuously welded rail. To simplify maintenance over miles of rail, special machines have been built that detect flaws in track, raise and align track, or clean and resettle track ballast.
Track gauge, or the width between the rails, varied tremendously in the early years of railroading. Gauges ranged from 3 ft (0.9 m) called narrow gauge lines to 6 ft (1.8 m) called wide gauge lines. Wide gauges were first believed to be more stable than narrow gauges, able to support broader cars without tipping over on curves. In mountainous areas or the highly populated urban regions of Britain, however, there was not sufficient room for wide gauge tracks, and rails were laid closer together. When it came time for the tracks of different railroads to merge into one enormous net, gauge discrepancies were a major problem.
The standard gauge was a 4 ft 8.5 in (1.7 m) spacing. Common in Britain, it was quickly passed along to other countries. In the United States, standard gauge became the official gauge of the American Railway Association toward the end of the nineteenth century. This led to changes in the rail spacing of narrow and wide gauge railroads, necessitating massively coordinated efforts in which the gauge of entire railway lines, as much as from 500 to 600 mi (804–965 km), would be changed in a single day.
Early cars were coupled together using a link-and-pin system. Given that the pins had to be put into place and removed manually while the cars were moved by a distant engine, coupling cars was a dangerous job that all too often led to the loss of fingers and hands. Alternate coupler designs were proposed, and in 1887 the Master Car Builders’ Association approved a coupler designed by American inventor Eli Hamilton Janney (1831–1912). Resembling the curled fingers of two hands, Janney’s coupler allowed cars to hook together without the use of pins.
Brakes, too, were a problem with early trains. They had to be applied on each car by hand, a time-consuming process. Brakemen on freight trains had the added difficulty of applying the brakes from a precarious perch on the top of the car while hoping that the train did not go under any low bridges. In 1869, American engineer and entrepreneur George Westinghouse (1846–1914) patented an air brake that used compressed air to force the brake shoes against the wheels. Each car had a reservoir of high pressure air (70–100 lb [32–45 kg]/sq in). A control pipe filled with compressed air ran the length of the train. If the pressure in the control pipe dropped, the compressed air in the reservoir applied the brakes. This could occur when the brakes were applied or when a car became detached from the train—an added safety measure.
When diesel and electric locomotives came into use, a different approach to braking was possible. Both types of motors can be reversed such that the motor is working against the motion of the train. This dynamic braking system allows minimal use of air brakes, with longer wear on the brake shoes. Some high speed trains have computerized braking systems. If the engineer exceeds permitted speed on a section of line, the brakes are automatically applied.
Locomotive brakes took much longer to catch on than railcar brakes. Robert Stephenson’s 1833 Patentee design included specifications for a steam brake, but the earliest recorded use of a brake on the driving wheels of an American locomotive was in 1848. Development and implementation was sporadic throughout the 1860s and 1870s but, by 1889, about one-half of all American locomotives were equipped with driving wheel brakes. By the end of the nineteenth century, locomotives were routinely equipped with brakes, a necessity given the increased power and speeds of the twentieth century engines.
In the early days of railroading, switches were set by hand and signal systems consisted of flags during the day and lamps at night. In 1856, an interlocking signal was designed to prevent signalmen from setting signals and switches in conflict with one another. In 1865, Ashbel Welch of the Camden and Amboy Railroad developed a new type of signal known as the manual block-signal. Trains were spaced apart by a prescribed distance, or block, and new trains could not enter this block until the first train left. The electric telegraph was used to pass the word that track was clear and the train ahead had reached the station.
Switch and train location information was conveyed to engineers by stationary signals such as flags, patterned disks that rotated between full view and edge view, or fixtures with semaphore arms. In 1871, electrical control of block-signals was introduced. In 1890, a compressed air switch with electronic control was installed on the Pennsylvania-Baltimore & Ohio railroad crossing. Fully automated switches soon followed in which the train wheels and axels made a complete conducting circuit, operating relays that ran the signals. The colored electronic lights used today are modern versions of these early signals.
Modern switching yards are largely automated. Car speeds are computer controlled and switching is automatic. Meanwhile, sensors and detectors check for loose wheels, damaged flanges, or other faulty equipment.
In 1964, the Japanese inaugurated the Shinkansen train, initially capable of going an unprecedented 100 mph (161 km/h). They have since built a net of high speed railroads across Japan. These trains run on special tracks and have had no fatalities since the opening of the system. Several derailments, however, have occurred at or above 170 mph (270 km/h). When these trains have run on traditional tracks, however, several fatalities have occurred, especially at line crossings. Europe has a number of high speed trains, from the Swedish X2000, capable of running at 136 mph (219 km/h) average speed, to the German Intercity Express. The French, however, are the kings of high speed rail transport. France, as of 2005, has about 745 mi (1,200 km) of LGV tracks, with four more lines currently proposed or under construction. The TGV trains run regularly over the countryside at nearly 200 mph (322 km/h). A special TGV train running over new track has reached an astounding 319 mph (514 km/h). Some TGV technology outside of France include the AVE in Spain, KTX in South Korea, Acela in the United States (which is run by Amtrak between Boston, New York City, Philadelphia, and Washington, D.C.).
At such speeds, the technology of railroads must be re-thought. Locomotive and passenger car suspension must be redesigned, and most trains must run on specially graded and built track. Engineers require incab signaling, as with average speeds ranging between 150 and 200 mph (241 and 322 km/h), there is not enough time to read the external signals. Brakes must be reconsidered. A train running at 155 mph (249 km/h) requires about 3 mi (4.8 km) to stop fully after the brakes are first applied.
A high speed option that is the topic of hot research is a non-contact, magnetically levitated (Maglev) train. Strong magnetic forces hold the train above the track. Such a train has virtually no rolling resistance or friction because there is no wheels and nothing rolling. The only impedance is that of air, making it extremely efficient.
Research and development of maglev trains has been vigorously continued in a number of nations, including Japan, Great Britain, Germany, South Korea, and France. All of these nations have developed a number of prototype vehicles that are moving into commercial operation. For example, Japanese engineers have designed a 27-mi (43.5 km) test line through the Yamanashi Prefecture that would carry up to 10,000 passengers per hour in 14-car trains traveling at 310 mi (499 km) per hour. Some German models have used a somewhat different form of magnetic levitation. The German’s Transrapid has nonsuperconducting magnets attached to the vehicle body and suspended beneath the guide rail. The magnets are attracted (rather than repelled) upward to the rail, lifting the train to within an inch of the guide rail. On December 31, 2002, the German Transrapid Maglev Train had its first commercially operated route in China from Shanghai’s Long Yang Road to the Pudong International Airport. It transports people
Adhesion —Frictional contact that makes the wheels of an engine grip the rails.
Boiler —A single tube or multi-tube vessel in which water is heated to steam.
Cylinder —A cylindrical tank into which steam is introduced to push a piston head back and forth, creating mechanical motion to drive the locomotive wheels.
Maglev —A non-contact (frictionless) method of train suspension in which strong magnetic forces are used to levitate the train above the track.
Rolling stock —Railroad cars. Rolling stock can contain such specialized cars as tank cars, refrigerator cars, and piggyback cars.
18.5 mi (30 km) in seven minutes, 20 seconds, at a top speed of 268 mph (431 km/h), with an average speed of 150 mph (250 km/h). The world’s first commercial automated Maglev system, called Linimo, began operations in March 2005 in Aichi, Japan.
As Maglev systems are constructed more frequently in the world, the costs to develop and maintain them will decrease. For example, the Shanghai Maglev train cost 1.2 billion dollars to completely build, which is about six dollars per passenger. However, as of October 2006, the use of Maglev trains in the world is limited to only a few sites. Most Maglev trains are still in the experimental and developmental stages.
Rail travel continues to be a safe way to travel when compared to automobiles. Annual death rates in the United States are regularly over 40,000, while rail fatalities are at about 1,000. However, regular rail service of passengers in the U.S. is relatively rare outside of the northeastern section of the country. Most public transit passenger rail service resides in New York City (New York), Chicago (Illinois), Boston (Massachusetts), Washington, D.C., Philadelphia (Pennsylvania), and Cleveland (Ohio). Amtrak operates the only passenger rail system in the United States. On the other hand, passenger rail service is very popular throughout the countries of Asia and Europe.
Railroads were a significant factor in the development of industry and are still a significant mode of transportation for goods and passengers. In terms of efficiency, they cannot be rivaled. While a diesel truck can haul a single or tandem tractor-trailer, a diesel locomotive can haul a string of loaded boxcars. As humans become more concerned about the environment and internal combustion engines are phased out, railroads are poised to assume an even larger role in transportation.
See also Mass transportation.
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