Right. Cost of building a new road on empty land: somewhat high. Cost of re-building it: really high. Road building didn't get wildly more efficient in the intervening years, now you have to pay both to build the new road but also demolish the pre-existing road, you have to do something about the hugely increased traffic loads which probably means you have to rebuild it whilst the road is live, which makes it far slower which increases your manpower costs, and lots more pipes and cables were laid below the road in the intervening years which have to be rerouted or handled in some way.