This tutorial shows how I made the banked corners for the oval in The Finish Line. Firstly I raise the outer part or the corner to a height say 2000uu. Continue you moving down in steps of about 250uu depending on how steep you want it to be. Next smooth them out as one so that they are not bumpy any more and you should get a nice banking. Finally smooth out the entry and exit so not to crash and we're done :)
Video showing it.