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A look at Automatic Train Stop (ATS)

By Noel T. Braymer

Since the disastrous collision at Chatsworth on September 12th, Metrolink has been in a panic to improve its public image and find quick ways to improve the safety of its trains. One step will be the rapid installation of Automatic Train Stop or ATS signaling on most or all of its train lines.


  These three pictures show the main components of ATS which is in use on passenger trains between Santa Ana and San Diego. At signal blocks with ATS installed you will see a bright silver bar alongside the tracks which is called a wayside inductor. On the trucks of the locomotives and cab cars are the sensors which activate the ATS as the trains passes a wayside inductor if there isn’t a clear or green signal.

ATS is considered an obsolescent signaling system and is 80 years old. Inside the locomotive or cab car the ATS detector is basically a magnet. As the train passes the ATS wayside inductor the sensor on the truck detects a magnetic field if there isn’t a clear or green signal. When this happens this turns on a buzzer and an eight second timer.  The engineer then must push a button to turn off the buzzer. If the button isn’t pushed within eight seconds the brakes will be applied and the train brought to a stop. The train doesn’t go into emergency braking. The ATS system primarily insures that the engineer is paying attention to the signals and is not incapacitated.