Idea: what about a track with two designers?
X builds the first half of the track, limited to 20-30 tiles (let's say on the left 15x30 half of the map) - and then, Y adds the second half, with about the same number of used tiles in the right half of the map. Car is Melange. (Akoss Poo and I had an online race like that several years ago.)
Nominations: X - Duplode, Y - Akoss Poo
I'm too lazy to build a track.