And self-driving cars may increase congestion yet. Whatever speed gains self-driving cars may attain by reducing time spent at a (now deprecated) traffic light

And self-driving cars may increase congestion yet. Whatever speed gains self-driving cars may attain by reducing time spent at a (now deprecated) traffic light or at an intersection/yield sign, people may just make more trips because road conditions have temporarily improved, thus cancelling that benefit. Say you decide not to drive to work but instead take the rail because you don't want to deal with the hassle of traffic. Maybe the rail has its downsides too, but they are acceptable to you. Now if self-driving cars makes highway congestion to work better, you may just be that person who switches from rail to car.