Building roads/highways is an incredibly complex and expensive process. There's an entire engineering dicipline that solely focues on just that. Highway geometric design alone is a headfuck, much less anything else lol
You can't just slap a bit of asphalt on the ground a call it a day, you need people with expertise.
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Geometric designs can be done pretty easily with software packages like civil3d. You put geographical data into the package and the software will pick the safest, fastest, and most cost effective route (limited cut and fill volumes) its kind of crazy.