Always check your train. You
might see that your train don't do any cash over the years. It might be
because of something like this.
You don't see that there is a track missing because of the trees.
The best way to prevent this sort of things is to look the first run of your train. If you destroy a rail because you are doing another one, change it now and don't say to yourself: I'll come back later. You might forget.
Ther can be one other problem.
The signals of the underground train may affect the upper train. Have a
The upper train can't go on because the underground train is "coming" his way
Even when the train is gone, the upper train can't go!