Braess's/Pigou's Paradox that more car lanes cause more traffic was found in the 1920's. We massively overbuilt for the car regardless and keep getting worse traffic to this day.
The paradox is that it _can_ cause worse traffic, not that it always does. American cities are built like shit for transport, but it's not as simple as "roads too big, therefore traffic". Sprawl is a much bigger (and more difficult to do ~anything about) issue.