Automated car fleets work well for suburbs.  But past a certain point, heavy rail train subways have far more throughput than the equivalent amount of cars.<p>Look at this image for example: <a href="http:&#x2F;&#x2F;imgur.com&#x2F;gallery&#x2F;v3ff7FY" rel="nofollow">http:&#x2F;&#x2F;imgur.com&#x2F;gallery&#x2F;v3ff7FY</a><p>Building &amp; maintaining roads and highways does take a lot of money too.   Building new roads vs building new railroad track on new land isn&#x27;t that much different cost wise.