SUBURBAN LOCALS HAVE A SYSTEM THAT STOPS THEM IF THEY ARE OVERSPEEDING
HOW THE AWS (AUXILLARY WARNING SYSTEM) WORKS

Taken from an article featured in Mumbai Mid-Day. Graphics by Deepak Ganatra.
The article is not featured on their site, hence reproduced here for the benefit of rail enthusiasts.

STAGE 1	When a local approaches a signal at high speed, the track magnet signals to the engine magnet about the error.
STAGE 2	If the local overshoots the signal and continues speeding, an intermittent hooter begins to sound on the Auxillary Warning System in the motorman's cabin
STAGE 3	If the motorman does not slow down or stop, the AWS applies an emergency brake bringing the train to a halt before the next signal.