The definition for Highway is:
A Road that is designed to enable Ground Vehicles to travel between relatively major destinations.
I've used highways to travel between obscure destinations (I recall some hot springs off California's Highway 1), and I suspect plenty of highway traffic doesn't start or stop at a relatively major destination. I propose:
A Road that is designed to enable Ground Vehicles to travel on routes that connect relatively major destinations.
Would "Three-Dimensional Paths" be better than "routes"?