Some signals also use physical mechanisms to make sure drivers obey them.

That signal can communicate with adjacent signals, ensuring that two trains do not try to occupy the same section of track at the same time. Infrared sensors, capacitance plates or short-circuits created by the cars' wheels can let a signal know when a train is present. Signals typically use colored lights to let drivers know when to stop, whether the track ahead of them is occupied and when to proceed with caution. Signs mark everything from speed limits to locations of fire extinguishers. Subway systems that don't use automated trains have an extensive collection of signs and signals to help drivers operate the trains safely. Sensors also detect objects near the train or in doorways, so people don't get caught between the doors or hurt themselves trying to board the train before it departs.Ĭommonly-used home signals, also known as interlocking signals

Two-way radio systems allow passengers to talk to employees in the control room or summon help in case of an emergency. Usually, automated subways also include surveillance systems, such as closed-circuit TV, to allow people to monitor trains' progress and safety from a control room. Computer programs keep track of where all the trains are, reducing the possibility of human error and improving the overall efficiency of the system. In such automated systems, a collection of sensors detects trains' locations in relation to one another. The trains will even have the capability to use brake heat to generate power.

These systems will control everything from the interior lights to navigation. The ongoing upgrade to the New York City subway will replace its older cars with automated cars, each of which will contain multiple computer systems. The subway in Copenhagen, Denmark, currently in construction, uses completely computerized, driverless trains. In some subway systems, the trains themselves, known as rolling stock, are extremely complex. This allows the subway to connect to other railways.īut a subway also requires several other systems that riders can't always see. In New York City, for example, the subway tracks' gauge is 4 feet, 8.5 inches (1.4 meters), which is the same as major railroad tracks. The train runs on rails, which often have the same gauge as other rail systems around the city. Most of the time, the train consists of several connecting cars that contain durable seats as well as poles and straps for people to hold on to when the train is full. At first glance, a subway is simple - it's a train that runs through a tunnel.

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