The effect that highways had upon the expansion of urban areas--rather then driving the price of existing urban land ever higher, the highways provided access to vast tracts of cheap rural land, triggering a vast expansion in the urban area. The demand for built space that had previously driven skyscrapers ever higher instead drove the urbanized area ever wider. As destinations became more widely separated, Americans are obliged to drive further and further, traveling more miles to make the same trip to the supermarket. Increasing trip length means more cars per mile of road, and thus more congestion, creating the demand for additional roadway right of way.
Eventually, congestion begins to create a 'time price' in the way distance once did, and proximity once again becomes valuable, driving up land prices near already desirable locations.