After testing the RedBull and Sonic Challenge circuits, and the article on how to use a starting rail and its Challenge lap counter, here is what is also possible with two Challenge GO circuits and “classic” GO rails in double track.
In the historical double track boxes, the same rail powers both tracks and only one rail is used to count the laps. In what I am offering you, we recover these elements in two Challenge boxes and we can dedicate an area for each driver. Each driver has his power supply and his lap counter in front of him.
Then you just have to figure out how to keep each lane independent on the circuit. Between the two starting rails, you insert a lane change that sends the driver to the second lane.
Then on the other side of the circuit you do the same thing with a lane change. In addition, this allows you to balance the lengths, during a lap; the cars are each their own inside the bend.
In the image, each lane is marked with a color to clearly differentiate the drivers.
Once you understand the principle, you can make more complex circuits according to your desires and the rails at your disposal.