Again, most cars in the game aren't racecars. And most players aren't into organized race clubs that worry about that sort of thing. I doubt most of us (that would be the hundreds of thousands, not the hundreds) even enable fuel consumption unless we are required to.
BTW, although a 20km square was originally promised back in 2013 when PDI was doing their presell of GT6, since then it was parsed to a 10km square, paraphrasing "due to limitations of the PS3". That's roughly a 6 mile square, not 10, ie, 36 square miles vs 100 square miles of space for containing such a layout, or said another way, only
36% of the available room you grossly over-estimate.
You: race car, significantly over-estimated maximum circuit length, and with fuel consumption on.
Reality: vast majority are far more "normal" cars, maximum coursemaker circuit lengths will be vastly shorter than what you contend, and most players don't enable fuel consumption unless forced.
Bottom line, for the tiny handful of PDI's customers who engage in routine, long duration racing with fuel consumption enabled in worst-case racecars, I'd suggest that you avoid designing courses that leave you sitting on the side of the road after less than a lap. Even a Monkey could figure that one out.

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