Your solutions are proportional reductions, a % reduction in the number of drivers. The problem of traffic rises with the ~2nd power of population because not

Your solutions are proportional reductions, a % reduction in the number of drivers. The problem of traffic rises with the ~2nd power of population because not only are there more people, there are more intersections. Intersections can only be solved with 3d roads, by eliminating overlaps. The bigger the city, the more artery roads you need with uninterrupted flow, and they eventually choke each other. Build tunnels and you can have point-to-point connections without choking off local flow. Reducing the number of drivers can't fully solve gridlock because at some point you have to hit a long light when you try to move from a high flow to low flow area. The only way to avoid that is with onramps and elevated freeways, but you can't build enough of those.