Setting something up which would run separately from FlightGear would require a separate computer to run it on.
Someone was making Motorcycles and tracks for them to run on which were made as custom scenery IIRC. That way the FG system could still run it. Maybe that would be the way to go. Find out who did the circuits and ask how it's done then make a small town with roads as custom scenery which we could all make use of.
Vic
EDIT: p.s. I think this subject should be a separate thread.