Transport Technology – Railways
Surface and underground railroads utilize more than 621,373 miles (one million km) of track worldwide. Trams, used for passenger traffic and trans porting goods, are an alternate form of rail travel.
Vehicles that ride on rails are more economical and can carry a greater payload than road vehicles. Their greatest disadvantage is that they are confined to the railway system and cannot reach some areas.
While there are various methods used to construct railways and tracks, they all follow the same basic pattern. Construction begins with a bed of crushed stone or concrete dampers in those sections where trains will operate at high speeds. Next, beams of wood or pre-stressed concrete are placed at regular intervals on the bed. The last step is to fasten the steel rails to the beams. The train cars are held to the rails by flanges on the wheels. The wheel-track connection is stabilized by the double frustrum formed by the joined right and left wheels.
International train service has been simplified by the extensive standardization of track width (gauge). Where different standards exist, as is the case near the border of Poland and Belarus, passengers and goods must change trains, or the entire car is transferred to a different chassis.
Propulsion
Trains are pulled or pushed along the tracks by locomotives. Locomotives can be powered in many ways, including diesel engines, steam engines, and electric power.
The diesel locomotives fall into three categories: diesel only, diesel-electric, and diesel-hydraulic. Electric locomotives acquire electricity through a bus bar or overhead contact line.
Current supply
Electric cars can be powered by either alternating current or direct current. Underground railways and trams are the primary users of direct current. Although heavy transformers are needed, most large electric railways use alternating current.
The heavy transformers are used to convert industrial network direct current to alternating current with a smaller frequency.
MAGNETIC LEVITATION TRAIN
As the name suggests, maglev, or magnetic levitation trains, are propelled by magnets: alternating fields moving ahead of the vehicle accelerate or slow it as needed. Since a cushion of air replaces the friction between track and wheels, significantly higher speeds are possible.
Maglev trains can also climb hills more easily. One problem, however, is the current lack of infrastructure, which is much more expensive to lay than ordinary train lines. Finally, because of its intensive energy use, this technology is not feasible for large-scale freight transportation.
Development of maglev trains by the Trans-rapid consortium began in 1969, but to date the only passenger track in the world is a short stretch in Shanghai.