I'll post this unfinished design, it was inspied by the suggestion of an arena circuit, so to try and give myself a scale to work within, I thied to find suitable venues or arenas that existed in the real world.
To give myself some space and to give the circuit some speed, it had to be fairly big, so I decided on the outline of a horse racing track with the assumptions that the inside would be flat, with raised grandstands giving a view over the whole circuit.
In hind-sight the bridge should just have been a double span as it's now very congested.
The Red arrow indicates where the pits and paddock would be - there would of course be viewing above the pit garages, across the whole circuit.
Oh and for reference if anyone wants to know, the race course is Cheltenham