[Tomptomp]

Federal law requires that the horn must be loud enough to be heard 8 miles away. You can notice when the train passes a crossing because the signal required is to blow two longs a short and a long.
Trains CANNOT stop in the distance they can see the way cars can. They rely on signals and track circuits to tell them what speed to do and sometimes the circuit can control the speed. ( ATO) automatic train control. The system never tells them that a car is on the tracks. I am sure you have seen the damage a train does when it collides with anything.
Also, trains can be a half mile long and communication between crew members can be made with engine whistles.
The first rule of railroading is : safety first in the discharge of duty. Communication is a must.