Glitch in Springfield Mountains

I found a really weird glitch in the springfield mountains...
if you go to the scenic area place thingo with the big kent brockman sign and a carpark, you can push cars off the road and through the railing! not only this, but if you are patient and push the cars through slowly, sometimes you go through with them and fall down in to the bottom of the ditch.
once you're down there, you can go through the side of it and your car will fly, and you can kind of see the whole map upside-down... keep flying around and somewhere there is a road that you can get onto, which isn't part of the map. it's short, but once you get on it there is a sign saying:

SOFT SHOULDER
BLIND CURVES
STEEP GRADE
BIG TRUCKS
GOOD LUCK!

does anybody know what this means (if anything)? id really like to know...