Blocking Volumes Map in VehicleGame Sample

In the Desert Rally Race - Vehicle Game Sample provided, they managed to align the Blocking Volumes around the splines of the tracks.


I notice the collision has its own map:

How did they manage to do that? I get you can do it by hands by manipulating the geometry of each volumes but I was wondering if there is a easy way to align and to snap them together like they did?

I know how to create a spline with a Messh along it but a blocking volumeā€¦?

How did they do it? :o