When building eight shaped tracks it is difficult to get the AIW right.
This tutorial shows how to solve this problem.
For this tutorial you need BTB and Guitarmans CAM-AIW editor.
The idea is simple: An aiw-file is nothing more than a string of waypoints including information about track and corridors.
This tutorial lets you pinpoint from which point the original waypoint string is replaced with an alternative string of waypoints.
Tutorial AI on 8-shape tracks 1.0
Solving slowing AI on an eight shaped track, when entering a tunnel or bridge.