The white signal aspect timer signal indicates that the train has to proceed at a certain reduced speed to clear the signal in a specified time.
The yellow trip arm next to signals is raised when the signal is red, and lowers when the signal clears. The arm will trip the brakes and put the train in emergency if a train rolls past the red signal.
The trip valve on the truck resets itself when it hits a trip arm. The motorman must put the trains' master controller and brake handle in the stop position when the train gets tripped. He/she then has to recharge the air in the brake system before the train will be able to move again.
Larry