When the player has made a mistake (ie two terminal command the same switch regardless of their defined positions), it is very bad and the GUI indicates it.
The block that can control the switch position using redstone
how you can use rail in your world
An example of configuration you can do to detect a cart in the detection zone in the last picture. It is delimited by two counter point that add axle when coming in and remove axle when getting out.
The GUI is almost the same except for the right down part that display 1 axle on the Axle counter point. You can remove or add axle manually with +- button and free the detection zone with 0 button.
When the player is greatly controling its terminal, there is no switch that is controlled by two terminal
when you click on controller block
When powered ans conflict error occurs : it outputs no redstone power
When powered and no conflict error : it outputs power (15)
The part of rail where we want to detect a cart. It is delimited by the switch on the right and an Axle Counter Rail on the left
The Axle counter point is not outputing any signal because the detection zone is occupied