How Trains Work

By: Craig Freudenrich, Ph.D.  | 
Vintage sepia tone photo of a train going through a desert
How did we get from this to bullet trains that reach up to 200 mph (320 kph)? duncan1890 / Getty Images

­Chugging across short distan­ces or entire continents, trains act as a major form of transportation worldwide. Also called railroads or railways, trains carry within their cars passeng­ers or freight — such as raw materials, supplies or finished goods — and sometimes both.


The History of Trains in the United States

Back before the wild ideas of people like the Wright brothers, Henry Ford and Gottlieb Daimler, you had limited options for traveling around town and country. Paved roadways didn't always crisscross the countryside. Even with roads, horse-drawn vehicles still struggled to move people and goods, especially in bad weather.

Pictured is a model of a railway carriage introduced on the Stockton & Darlington Railway. How did we get from here to high-speed trains?
Time & Life Pictures/Getty Images

As early as 1550, pragmatic Germans constructed and used wooden railway systems, reasoning that horse-drawn wagons and carts could travel more easily and quickly over wooden rails than dirt roads. By the late 1700s, iron wheels and rails had one-upped wooden ones.


­But it wasn't until early locomotives were invented in 1797 in England that the railroad as we know it began to take shape. The Stockton & Darlington Railroad Company in England became the first public railroad to carry passengers and freight. Steam locomotives carried six coal cars and up to 450 rail passengers a distance of 9 miles (14 kilometers) in less than an hour. Horses could no longer compete with rail transport.

Across the ocean, the Baltimore and Ohio Railroad Company established itself as the first U.S. railroad company in 1827. It didn't take long for the railroad industry to boom. By 1860, U.S. rail workers had laid more than 30,000 miles (48,280 kilometers) of track, more than in the entire world [source: AAR]. Railroads served as the main mode of transportation and made it cheap and easy to ship supplies and goods, even for Union and Confederate armies during the Civil War.

After the Civil War, the U.S. railroad network expanded again, and the country's first transcontinental railway was completed in 1869. Towns sprouted along the railway lines, and the railroad hastened westward expansion. By the early 20th century, U.S. railroads operated 254,000 miles (408,773 kilometers) of track. Diesel locomotives had replaced steam ones.

But by the mid-20th century, the decline of the U.S. railroads had begun. A developed interstate highway system and extensive federal regulations took their toll on trains. In the ongoing energy crisis, however, trains, which run on diesel and som­etimes even biodiesel fuel, may regain their former popularity with passengers as we move through­ the 21st century.

­Don't get derailed. Stick around as we talk about train technology, how trains move people and freight, and what the future of rail transportation may hold.


Full Steam Ahead: Locomotives and Train Technology

When we say train, we don't just mean a Thomas the Tank Engine. Rather we're referring to the whole package: railroad cars, railroad track, switches, signals and a locomotive, although not all trains rely on locomotives to pull them, but most of the trains we'll mention do.

With the locomotives leading the way, coupled-together railroad cars follow, filled with freight and passengers — even circus animals in some instances. The railroad track steers the train and does a few other things that we'll talk about later. Because many trains operate on the same track, switches and signals control the traffic. Let's break it down.


The job of the locomotive is to change the chemical energy from the fuel (wood, coal, diesel fuel) into the kinetic energy of motion. The first locomotives did this with a steam engine, which you can read more about in How Steam Technology Works. The steam locomotive lasted for about a century, but was eventually replaced by the diesel locomotive, a mighty mechanical wonder that may consist of a giant engine along with electric alternators or generators to provide electrical power to the train. In fact, diesel locomotives have their very own article — How Diesel Locomotives Work. Many trains intersperse multiple locomotives throughout their lineup to increase and distribute the power.

Besides steam- and diesel-powered locomotives, many modern trains operate solely on electrical power. They get the electricity from a third rail, or electrical line, along the track. Transformers transfer the voltage from the lines, and the electrical current drives the motors (AC or DC) on the wheels. Electrical locomotives are used on subways and many commuter rail systems.

Operators control the train by using the throttle, reversing gear and brake. The throttle controls the speed of the locomotive. The reversing gear enables the locomotive to back up. The brake allows the locomotive to slow and stop. Regardless of the type, locomotives use air brakes and hand brakes to stop the engine.

Air brakes use high-pressure air to drive the brake foot against the wheel. The friction between the brake pad and the wheels slows the wheels' motions. The operator also throttles the engine back to slow the train, like when you take your foot off the gas pedal when stopping your car. A mechanical hand brake is also used in case the air brakes fail (usually when there's insufficient air pressure to drive them).

All railroad cars have an undercarriage that contains wheels and a suspension system to buffer the ride. On each end of the undercarriage, couplers, which are like hooks, connect the cars.

What's on top of the undercarriage depends upon the type of railroad car, and there are several.

  • A boxcar is a basic box into which crates of goods can be piled up.
  • An ore car has an open top and carries coal or other mineral ore such as bauxite.
  • A tank car holds liquids, usually chemicals such as chlorine and ammonia.
  • Flat cars can hold bulky irregular items on them, such as construction equipment or spools.
  • Trailer cars can transport automobiles.
  • Container cars are filled with boxed containers of various materials. Often, containers can be double-stacked on these cars.
  • Passenger cars, of course, hold people. Some have glass-enclosed viewing areas on top, and some may even be sleeper cars for long trips.

Keep reading to learn about what guides trains on their travels.


Keeping Us in Line: Train Tracks

The ties in these train tracks near Queensland, Australia, are wooden, and the rails stretching into the distance look to be made of steel.
Tim Graham/­Getty Images

Railroad tracks guide the train, acting as the low-friction surface on which the train runs and often transferring the weight of the train to the ground below. The track may also provide electrical power along the third rail, as you'll recall.

A railroad track consists of two parallel steel rails set a fixed distance apart, called the gauge. The standard gauge is 4 feet 8.5 inches (1,435 millimeters). The rails are connected to each other by railroad ties (called sleepers in Europe), which may be made of wood or concrete. The rails are usually bolted to the ties. The ties are set into the loose gravel or ballast. Ballast often consists of loose stones that help transfer the load to the underlying foundation. The ties "float" on the ballast and the weight of the track keeps them stabilized.


When rail workers are laying train tracks, they often use a flat-bottom steel rail that resembles the steel I-beam girders of construction. The rail has a wide base or foot, a narrow web and a head (wider than the web, but not as wide as the foot). The weights of the rails vary from 80 to 160 pounds (36 to 73 kilograms) per yard depending upon the type of train operating on the tracks and the country. Segments of rail track may connect to one another by bolted plates called fishplates, but most modern rail segments are welded together to provide a smooth ride.

Beneath the rails, the track is sometimes cushioned or ballasted. The foundation may be made of sand or concrete. In many cases, railroad tracks are elevated above the surrounding ground and have drainage systems to remove water. They may also be surrounded by fences to prevent animals and people from wandering on to the tracks. Finally, electrical trains will have either a third power rail or overhanging wires that supply the electricity.

­Steel tracks can be straight or curved to steer the train since steel is easily bent into shape. Depending upon the topography, some curves may be slightly angled or banked to help the train stay on the track as it negotiates the curve. At various points along the track, rails may have switches, which can move a train from one track to another. Switches and accompanying track are important for controlling traffic. For example, when two trains are operating on the same track, a switch can allow one train to pull off to a holding track while the other one passes. A switch also can change a train's direction like moving it from a north-south track to an east-west one. Many railroad stations have switching yards where trains are assembled and moved onto various tracks.

Finally, signals along the tracks keep the train operators informed of traffic conditions ahead. Signals control train traffic much like traffic lights control automobile traffic on roads. Besides signals, many locomotives have radios and computer terminals that monitor traffic conditions using information supplied by signaling centers, which are similar to air traffic control stations.

Now that we have the mechanics down, let's see how they fit together to move packages and people.


Freight Railroad Systems

This Wyoming freight train's open-topped ore cars are filled with coal, a common load for freight railroads.
Michael Melford/­Getty Images

­Railroads are perhaps the cheapest way to haul freight overland. According to the Association of American Railroads (AAR), U.S. freight trains lead the world in volume of traffic, amount of freight hauled, revenues, affordability, miles of track and other measures.

U.S. freight rail include the following categories:


  • Class I freight railroads report revenues greater than $346.8 million. There are seven U.S. freight railroads, and they haul more than 67 percent of the nation's freight. They operate 3,200 to 32,000 miles (5,150 to 51,499 kilometers) of track and typically engage in long hauls. Some companies in this class include CSX Transportation, Norfolk Southern and Union Pacific Railroad.
  • Regional freight railroads check in with revenues between $40 million and $346.8 million. More than 33 regional railroads operate in the United States, each with 350 to 600 miles (563 to 966 kilometers) of track.
  • Local linehaul freight railroads have revenues less than $40 million and operate fewer than 350 miles of track. Many local linehauls transport freight within a 75-mile (121-kilometer) radius, often within a single state. About 324 local linehauls function in the United States.
  • Switching and terminal (S&T) railroads don't provide point-to-point transportation but rather provide switching services. They pick up and deliver cars within an area, usually for local linehaul railroads.

[source: AAR]

Freight railroads carry lots of stuff, but the most common item is coal for electrical power plants (44 percent tonnage and 21 percent revenue). Chemicals, farm products, nonmetallic minerals, mixed shipments and other commodities make up the major categories. In 2007, Class I railroads hauled more than 1.9 billion tons (1.7 billion metric tons) of freight and earned about $53 billion. Freight railroads make money based on the weight of freight and the distance traveled. The industry uses the ton-mile as the basic unit, and Class I railroads carried more than 1.7 trillion ton-miles in 2007 [source: AAR].

­In the United States, the railroad companies themselves own the railroad tracks. Land grants by the federal government to the railroads in the 1800s allowed the railroads to own the tracks. Furthermore, U.S. freight railroad companies are privately owned and operated, with no government subsidies. While railroads own some of the thousands of freight cars used, car companies and other shippers actually own most of them.

The international leaders in freight railroads are the United States, Russia and China. In contrast to the United States, European railroads are mostly government-owned. They primarily transport passengers and, to a much lesser degree, freight. However, this setup is changing, and hauling freight is becoming increasingly important. European railways don't make as much money hauling freight as their U.S. counterparts do. Their situation seems to be similar to that of U.S. freight railroads before the Staggers Rail Act of 1980 was passed.

On the passenger front, however, European railroads are millions of meters ahead, as you'll read about next.


Passenger Railroad Systems

The lounge on Amtrak's Coast Starlight train looks pretty comfortable, so why aren't more people riding on the only nationwide passenger railroad in the United States?
Lee Foster/­Getty Images

­Early on in U.S. train travel, freight railroads offered passenger services, but didn't make much money. In 1970, Congress created Amtrak to take over passenger services from the freight railroad companies. Amtrak operates corridor services amid major urban areas on the East Coast, Midwest and West Coast. It also offers cross-country services.

Amtrak operates on tracks owned by host railroads. In fact, 70 percent of Amtrak routes are owned by Class I freight companies. It serves more than 500 destinations in 46 states. In 2007, Amtrak carried 25.8 million passengers (average of 70,000 passengers on 300 trains daily).


Amtrak receives federal, state and local support in return for offering passenger and commuter services. Despite the government support and increased ridership, Amtrak hasn't turned a profit. In 2007, Amtrak's expenses exceeded its revenues by about $1 billion. One potential reasons for the shortfall is the fact that Amtrak faces steep competition from automobiles and airlines, but more about that later.

­In contrast, European railway systems are devoted primarily to passenger traffic. Most European railways are government-owned. In 1959, the Eurail Group was created to handle the increased tourism load. The organization coordinates and markets passenger rail traffic among 30 European countries. The European network connects most European cities. Eurail's high-speed trains have become competitive with airlines and are more efficient than automobiles.

Russia, China, Korea, Japan and Australia also offer passenger rail service. Each country has an extensive rail network for passenger travel. Furthermore, the European train network is being linked to railways that travel to China, India and Southeast Asia. However, not all countries or continents have established international rail networks. Neither Africa nor Central or South America boast such networks. And while Mexico, Peru, Brazil, South Africa and Morocco have trains, those trains operate on tracks located solely within those countries.

We can't let this page end with mentioning a few of our favorite famous passenger trains.

  • The Orient Express was one of the first luxury trains. In 1883, it carried passengers from Paris to Giurgi, Romania. The Simplon Tunnel expanded the train's service to Venice in 1906. By 1923, the train's route lengthened again to reach Istanbul. Its popularity peaked in the 1930s, but travel declined after ­World War II. Its last trip was in May 1977. Agatha Christie's favorite train was reborn in 1982, and its travel route from London to Venice was re-established.
  • Eurostar became the first railroad to link the United Kingdom with the European mainland. It travels through the Channel Tunnel that extends under the English Channel. Eurostar offers high-speed train service from London to Paris and Brussels. You might remember Eurostar from its cameo in the movie "Mission Impossible."
  • TGV, the French, electrically powered high-speed train, whizzes among Paris, Lyons, Bordeaux and Marseille. In April 2007, it set the world record for fastest train travel at 357 miles per hour (575 kilometers per hour). It routinely travels at 200 miles per hour (320 kilometers per hour).

Will train travel catch on in more than a few select countries? Keep reading to find out.


The Future of Train Transportation

High-speed trains like France's TGV train may dominate the rails in the future, but occasionally they get in spectacular wrecks, too, just like a regular old train.
Michael Dunning/­Getty Images

The success of the U.S. freight railroad system has shown that moving goods by rail can be economical, efficient and profitable. Trains are an essential part of a country's infrastructure, so what does their future look like?

The future of train transportation will be dictated by the price and availability of oil, the determination of governments to find alternate modes of travel and the public demand for economical, fast transportation. For example, Europe's high passenger rail traffic was driven in part by historical precedent and the price of gasoline. It has improved with advancements of high-speed trains and dedicated passenger railway lines.


In the United States, passenger rail traffic hasn't caught on for several reasons:

  • The country lacks a passenger rail network that's independent of the freight railroad system, so not all areas of the country have access to railroads.
  • Until recently, the price of oil has still been relatively cheap, which makes automobiles and airlines more desirable modes of transportation for many people.
  • Many trains are still relatively slow or make many stops. For example, a train trip from Raleigh, N.C. to Washington, D.C., can take five hours, which is the same amount of time that it takes to drive between these two cities.

However, as oil prices increase, Americans will seek alternative means for long-distance travel, and trains are a good candidate.

But retooling U.S. railroads for passenger traffic won't be easy. For example, travelers will most likely want high-speed trains like those in Europe and Japan. But high-speed trains are expensive to build and maintain. They also work best on dedicated passenger railways. Furthermore, the railways must reach more cities and destinations than they do now. So, making railroads a major form of passenger transportation will require investments to expand and improve the railway systems. Whether this expansion will be done by the government or private companies remains to be seen. And it probably won't happen until public demand for passenger rail transportation increases.

New technologies such as magnetic levitation or maglev trains may increase train speed even more. These trains don't have wheels but rather travel on superconducting magnetic rails, but they're expensive to build and maintain.

Keep chugging along for more interesting train stories, like How the Great Train Robbery Worked.


Train FAQs

How do trains move?
A train is a whole package of railroad cars, railroad tracks, switches, signals and a locomotive (although not all trains rely on locomotives to get them moving). The locomotive, first, changes the chemical energy from the fuel (wood, coal, diesel fuel) into the kinetic energy of motion. Operators use the throttle, which controls the speed of the locomotive to reverse gear and apply the brake.
How do trains run on tracks?
A railroad track is made up of two parallel steel rails set a fixed distance apart, called the gauge. The rails are connected by railroad ties, usually bolted to them. The ties are set into the loose gravel or ballast, which typically consists of loose stones to help transfer the load to the underlying foundation. The ties "float" on the ballast and this is how the weight of the track keeps them stabilized, allowing trains to run on tracks.
Do electric trains have gears?
Modern locomotives use electric traction instead of gears as electric traction is much more flexible than gears. Diesel fuels generators from the combustion engine and transform the energy using an alternator, which runs the traction motors.
What is the distance between rails on a train track?
A train track consists of two parallel steel rails set a fixed distance apart, which is called the gauge. The standard gauge is typically 4 feet, 8.5 inches (1,435 millimeters).
How does an electric train work?
Many trains operate solely on electrical power. They get the electricity from a third rail, or electrical line, which is present along the track. Transformers transfer the voltage from the lines, and the electrical current enables the motors on the wheels to move. Electrical locomotives are usually used on subways and many other commuter rail systems.

Lots More Information

Related HowStuffWorks Articles

More Great Links

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