A big part of the reason for the right angles paths of Detroit area freeways has to do simply with the fact that the property and township boundary lines were originally laid out in squares subdivided into rectangles. So it was easier and less expensive to acquire land for freeways along the existing property lines and road alignments. South of Big Beaver I-75 mostly runs along the old Stephenson Highway alignment, which was originally laid out and acquired as a streetcar/interurban right-of-way, complete with the now much hated 9 Mile curve.