Editing Mission Builder (section)

==== Car Paths ====

The simplest maps (which is most of them) have a single car path that follows a single road across the map.  These are by far the easiest to make.  Make a path just like you would for the race track, but instead of a loop you want a single line from one edge of the mission area to the other.  The AI will head the first waypoint on the next repeat of the map when they get to the last waypoint on this repeat, so make sure the two points are close to each other.  You also need to make the points big enough that the AIs won't miss them if they're driving slightly off road.

More complex maps may have multiple car paths that join and split it complex ways, but I can't help you there.  Have a look at the gates of SS if you want an idea of how bad it can get.  Then just stick to making maps with a single road on.