Both rapid transit and light rail systems are powered by electricity in some form. The rail systems are incorporated into a city's electrical grid and powered by huge electric conductors that run along the tracks throughout the system. These conductors are called the "third rail." Rapid transit and light rail systems may also use overhead wires, magnetic levitation, monorail and fourth rail technology for propulsion.
Another similarity between rapid transit and light rail is that both transportation systems are most often funded and operated by the municipal government of the area where the system is located. The public transportation authority of the municipal government oversees the upkeep, daily operations and expansion of all public transportation. Taxpayer revenue as well as direct passenger revenue funds the maintenance of public transportation as well as any future projects that the government deems necessary.
Rapid transit and light rail also share similar design structures. Both systems consist of rail lines that travel along set routes to various stations throughout the city. Different lines and stations are usually designated by different colors, names and numbers. Rapid transit and light rail lines are configured to provide passengers in high-volume areas of a city with convenient access to other high-volume areas. Rapid transit has one major structural difference from light rail in that rapid transit may be partially or completely underground -- in which case it is called a "subway"; light rail systems never go underground.
Rapid transit and light rail systems have similar methods of operation. Both systems are often heavily automated, but not fully automated. This means that both systems are operated by advanced, large-scale computer systems that regulate the timing of the train and track controls, but also have at least one human worker managing the computer system. Each train also often has a conductor at the front. Rapid transit and light rail systems vary in the amount of automation each will incorporate; with some being almost fully controlled by humans and some having only one person manning a large computer system.
