It's good to challenge yourself in the editor. Normally I test drive every turn as I build and I let the car tell me where it wants to go... where it feels like it should go. And I think you can end up with a very flowing track if you follow that workflow.
However, I wanted to see how good of a track I could pull off with absolutely no test drives. I would build the entire track from start to finish, including scenery and signage, without driving it at all.
So I started, and I found that it was actually incredibly fun to just place block after block after block. Sure, I imagined the car on the road and I tried to make sure I didn't place blocks in a way that would make it difficult for the car to navigate. But I wasn't constantly jumping back and forth to test each section of track. I found it incredibly liberating and a building experience that is unlike anything I've had before.
It took me about 5 hours to build this track, with a short break in the middle.
The track has a few rough edges, but overall I think it turned out pretty well.
Author Time is 8:20 but it should be easily beatable, as I had some crashes in there.