No, that is still only the short term new equilibrium. What happens is that roads with unused capacity (or at capacity, but acceptable congestion) get busier as

No, that is still only the short term new equilibrium. What happens is that roads with unused capacity (or at capacity, but acceptable congestion) get busier as activity increases around those roads, because of the excess capacity/low congestion. Of course it's more complex than just that; it heavily depends on the spatial relationship with job activity centers within commuting distance, social expectations, economic characteristics and many more, but the core tenet remains - adding roads is not a long term solution for congestion, spatial planning is.