what's an "insim layout"?
The cruise servers use a layout (which anyone can make, it's a just a question of putting barriers and cones on the track. Making a playable layout however is a different matter) to define the rights of way.
Separate from this is that they use a separate program that interfaces with LFS via Insim. Afaik some of the programs are custom, one-off creations by those with programming skills. Some use an off-the-shelf application, I think LFS Lapper is one such thing.