My current development focus is realistic style race tracks. They are based on eiter fantasy or real locations, but actual track design, layout and infrastructure is mostly fictional. Apart from New York city circuit, which is a take on "What if someone decided to use these streets as city race event". Kind of a prototype of what could be made.
This is the gallery of my Realistic Race Track models available, with new locations added every month or two. All models are royalty free to use in your game project, animation or visualization. Purchases can be made either in Unity Asset Store, or FAB store. You will find links to stores on page of each track.
Unity Asset Store downloads include texture files in .PSD format with unlocked layers. This will allow you to make any modifications necessary to make the track look individual to your project.