It is a natural consequence of the evolution of our transportation system that the gentlest slopes have become the primary routes for cars. The terrain dictated those as the natural choices for routing before cars even existed. And once cars came along, these routes were widened and often landscaped to ease travel through them. In some cases, such as the W&OD, it was a railroad instead, which then fell into disuse once cars and trucks began to dominate transportation.
