I'm really hoping that whatever effect occurs when the train leaves the launch tub is very pronounced.
I imagine a strong set of LEDs or even a low powered spotlight of some sort that would create a shaft of light that would act as visual for gamma radiation spewing from the tube. Even better would be if the station building and tube lighting began to pulse faster and faster as a train was cleared to leave the station and went through the tunnel sequence, then returned to the normal slow pulse after the effect occurred.