And we just passed the half of this 10 part series :) For this one, you can see that there were no light trails in the basic exposure. They were all added from the other, brighter exposures during manual blending.
This is the final photo, open the full post to see the original shot and how it looked in photoshop:
Light trails

This is what I started with:
Then is how all the layers in Photoshop looked like: