Rail lines have more than 10x the throughput though, so you need vastly less of them to do vastly more work. A city with enough roads for 100% car usage is app

Rail lines have more than 10x the throughput though, so you need vastly less of them to do vastly more work. A city with enough roads for 100% car usage is approaching not being a city anymore, just an unending suburban hellscape, but a city with barely any roads and more rail than it really needs can still be a beautiful city. To add to that, underground railways exist in many cities, but underground road networks effectively don't. The throughput by volume dug out the ground is viable for a rail service, its totally non-viable to bury an equivalent throughput 20 lane highway underground.