When testing modifications for a circuit using AI, it can be tedious to wait a long time each time for the train concerned to arrive where the modification takes place. Would it be possible to have an "accelerated" mode?
From the Surveyor or Driver Main Menu select Settings --> General Settings and tick Enable Debug Features.
Then, when in Driver mode, hold down the Shift key (either one) and Trainz will go into warp speed. You may get a message from Windows about turning on "Sticky Keys". I cancel that request and there is a way of turning that Windows feature off so it does not bother you again (but I cannot recall how).