It's called an alerter, and i believe it has to be installed on all modern locomotives, or retrofitted on older ones. possibly some historic units don't require them much in the same way vintage automobiles might not require seat belts...
in freight service it usually has a 25 second time from the time the light starts flashing (a beeping follows a few seconds after the light and grows progressively louder) until a penalty brake application is made and the throttle is cut out. a penalty application means the air from the brake pipe starts to exhaust at a service rate, slowing the train to a gradual stop by increasing the pressure of the brake shoes against the wheel. this is not the same as an emergency brake application which results in the air exhausting from the brake pipe as fast as possible, thereby squeezing the pads to the wheels as hard as possible.
some might ask why the alerter wouldn't apply the emergency brakes, and the answer is simple: in passenger service, you would have meatbags suddenly thrown forward in the carriages, and in freight service (think heavier loads) the possibility of a derailment or damage to the track structure goes up considerably. brakes on the train apply serially, so the rear cars on a train will continue their forward momentum for a few seconds after the cars ahead of it. if you had loads on either side of an empty car or block of cars, the empties would pop off the rails quite easily.
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the simplest answer is "still on the surface of the earth," of course. everything else is an overreaction based on irrelevant information.
It's called an alerter, and i believe it has to be installed on all modern locomotives, or retrofitted on older ones. possibly some historic units don't require them much in the same way vintage automobiles might not require seat belts...
in freight service it usually has a 25 second time from the time the light starts flashing (a beeping follows a few seconds after the light and grows progressively louder) until a penalty brake application is made and the throttle is cut out. a penalty application means the air from the brake pipe starts to exhaust at a service rate, slowing the train to a gradual stop by increasing the pressure of the brake shoes against the wheel. this is not the same as an emergency brake application which results in the air exhausting from the brake pipe as fast as possible, thereby squeezing the pads to the wheels as hard as possible.
some might ask why the alerter wouldn't apply the emergency brakes, and the answer is simple: in passenger service, you would have meatbags suddenly thrown forward in the carriages, and in freight service (think heavier loads) the possibility of a derailment or damage to the track structure goes up considerably. brakes on the train apply serially, so the rear cars on a train will continue their forward momentum for a few seconds after the cars ahead of it. if you had loads on either side of an empty car or block of cars, the empties would pop off the rails quite easily.