That's underselling it a bit. The growth rate of roads was deliberately stalled in the 70s. We just elected not to build new infrastructure in most places, and coast with what we had. There are some exceptions, but they are just that -- exceptions.
Meanwhile, it seems that the same people who didn't want to build any more road infrastructure also didn't want to build mass transit rail infrastructure either. And so here we are.
Now, it's probably too late without a major cultural shift and realignment of priorities and sensitivities. We give everyone a seat at the table and every last one of them has veto power. So ... nothing happens. Without unanimous consensus.
Hell, Oregon & Washington spent $175 million just to plan out a new bridge, and over $100 million of that was just pretty pictures. In the end, too many vetoes, too much fighting, we gave up. Eventually we will try again but maybe it will take the existing I-5 bridge dropping into the river from old age before agreement can be reached.