Step #1 -
Click the 3D Snap Button. Step #2 - Select Vertex.
Continue
below.
Create a spline around your track (inside or
out).
Step #3 -
Click "create" button. Step #4 - Click "shapes" button. Step
#5 - Click "line" button. Step #6 - Create your spline using
these properties.
Step #7 - Just
draw your line around you track (inside or out -- which ever you
need a wall for.) Your line should "snap" right into place if you
set the "3D Snap Toggle" correctly.