Elevated Transit Technology

Elevated transit consists of trams, trains, and monorails operating at some vertical distance above ground level. They are usually part of a commuter system associated with metropolitan area, but there are also many small scale and private examples as well. Elevated transit systems are dependent on a number of technologies, the most important being an elaborate system of sensors to monitor the speed and position of rolling stock. You are probably familiar with motion sensors from driving your car. Say you own a BMW sedan – items such as a BMW ABS sensor detect whether your brakes are in danger of locking up.

Elevated transit cars are normally powered by electric motors and ride on steel wheels. The wheels fit onto two steel rails and guide the train's path. There is a third rail that provides the traction power to the electric motors. Third rails typically carry up to 750 volts, and can be quite lethal. Occasionally, elevated transit systems use overhead electric wire instead of third rails, allowing for higher voltages and more efficient operation. However it is supplied, most electrical sources for elevated transit systems are direct current (DC). This means that large rectifiers are needed to power the DC motors. Some newer systems use alternating current (AC) instead.

Tracks are usually standard gauge, though monorails use one central track instead of two peripheral ones. Monorails can straddle a track from above or hang from a suspension rail. Some systems use rubber tires on rollways made of steel or concrete.

Until the 1960s, all elevated transit cars were driven by humans, and many still are. However, automated systems now drive many smaller and newer systems. These systems maintain proper speed and pacing of cars to optimize service. As mentioned above, a sophisticated sensor system is used to avoid accidents and track car movement. In human-driven trains, a system of signals tells the driver whether to proceed at full speed, reduced speed, or to come to a stop. Any signal malfunction can have fatal repercussions, so continual maintenance is performed.

Going back to our BMW car example, BMW power steering reduces the effort in controlling the car's path. Trains however just follow their tracks, so you can say they are steered automatically by their rails. If an elevated train jumps its tracks, it may tumble to the ground killing or injuring hundreds of passengers.