Trams in Frankfurt, Germany, will soon carry electronic assistance technology that warns their drivers of potential collisions and brakes independently if the operators fail to respond quickly enough.

The collision warning system, developed by Bosch, combines radar and video sensor technologies derived from the company's automotive division together with a rail control unit. A radar sensor, with an aperture of up to 70 degrees, monitors the area up to 160 meters ahead of the tram and measures the speed and distance of cars, buses or other trams.

If the system detects that an object is too close, it gives the driver a visual and an acoustic warning. Image source: BoschIn addition to mobile obstacles, the radar sensor detects static objects such as buffer stops. A video sensor complements the radar technology, watching for anything crossing the tracks. The central rail control unit processes information from both sensors, along with other factors, such as the speed of the tram, to provide a detailed image of the environment.

If the system detects that an object is too close, it gives the driver a visual and an acoustic warning. Should the tram driver not react to the warning signals within two seconds, the automated system slows the tram to a stop.

If triggered, the automatic braking action is intended to be gradual so that passengers who are standing will not lose their balance. If necessary, drivers can deactivate the braking operation or increase the braking power, depending on how critical the danger is perceived to be. This leaves tram operators in control of any situation, but with assistance from the system's electronic eyes and ears.

According to Bosch, the technology represents "the first step" toward automated trams.