<i>Self-driving cars may lead to marginal improvements in road throughput, but shared-vehicle transportation will always be able to move more people in the same amount of space.</i><p>It&#x27;s not useful to &quot;move more people in the same amount of space&quot;  if those people are going to end up someplace other than where they need to be.  Classic case of optimizing the wrong parameter.<p>You can&#x27;t apply 19th-century rail route design to 21st century transit problems... well, you can, but it&#x27;s never going to be optimal.<p><i>Self-driving cars may lead to marginal improvements in road throughput, but shared-vehicle transportation will always be able to move more people in the same amount of space. If a transit route has sufficient ridership to justify investing in rail, it is already going to be very congested at commuting hours, and will remain so after self-driving cars become common.</i><p>The whole roadway system can be a &quot;transit route,&quot; with the proper planning.  A fleet of autonomous vehicles <i>is</i> a train... but one that has none of the drawbacks of fixed routes.