I have edited the .GBD file and the objects do form shadows and the vertical terrain dose look darker, but if you notice the shadow coming from the man in the Kart, well the top section of road is 2 meters above the section of road that the Kart is on, so in real life you should see a shadow on the lower section of terrain and track, that is longer than the shadow that is coming from the man in the Kart
It will all be dependant on the angle of sun that the game is being told to produce.
To get your shadows absolutely perfect (and this is something i`m working on), your track`s X axes has to be parallel to North, and also have the correct longitude entered for the location of your track, the time of year and the north direction.
I`m still learning to understand all of this suns azimuth stuff, so dont be surprised if i cant answer your questions (if you have any), but as it is for many other, this is still on the learning curve for me.
EDIT: what time of day were you running at in that picture?
I think I understand about the sun, time and longitude, I think this picture will explain a little better.. if you notice the bollards on the higher level of terrain, you can see the first part of their shadows on the chamfer of the high level terrain and then you can see the rest of their shadows on the road of the lower terrain, but you should also see the line of the edge of the high level terrain on the low level terrain that would join up the shadows of the bollards on the low level terrain..
I have the longitude set at 60 to produce long shadows and time of day is 12:00
I don't think you can get terrain to make shadows in BTB.
I would suggest placing an object in the same position as your terrain.
Set it to cast shadows but not to render.
Then it should make a shadow over your track.