How Trains Work

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.

Mouse over the part labels to see where each is located on the diesel engine.

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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 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.

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

­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.

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

U.S. freight railroads include the following categories:

[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.

­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.

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

­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:

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.