You absolutely could build your way out of highway traffic given sufficient lanes. However, given the constraints of land and how density inefficient cars are, you'd have to build double or even triple (etc) decker highways all over the place, which is totally economically infeasible.

Meanwhile, you can build a shitton of lanes out in the exurbs, sure, but then all the cars on your thirty lane highway have to go somewhere when they get into the city and land is a lot more scarce.