Tl,dr: If the US is going to give up personal driving, it needs fast intercity connects and ubiquitous in-city transportation.<p>- Subways and light rail are high cost, high visibility, negative return investments for most municipalities.<p>- Intercity could be trains or a hyperloop, given hyperloop developers&#x27; projected cost structures.<p>- In-city should be buses and, eventually, self-driving quasi-taxi fleets.<p>----<p>On the in-city transportation:<p>Subways are very expensive to build, very expensive to move, and a deficit on their community if the areas in which they&#x27;re built don&#x27;t have very high population densities.<p>See: almost any city in the US with a subway, many cities elsewhere.<p>----<p>Light rail, if the tracks are built into existing roads, is a little less expensive to build and move but suffers the same population and planning issues as subways, as well as being an added impediment to traffic and imposing the same commuting inefficiencies on the rider as if they were in a car.<p>If they&#x27;re instead given dedicated space, they become much more expensive as extra road lanes must often be built (or easements otherwise negotiated and purchased by municipalities), and they end up much harder to move for want of further easement &amp; road expansion.<p>The light rail requiring expansion of paved traffic surfaces would also make them less environmentally friendly from the perspective of urban surface radiance.<p>See: The Arlington&#x2F;Alexandria, Virginia light rail project most quickly comes to mind.<p><i>I&#x27;m looping &quot;trams&quot; in here as well because I&#x27;m assuming they&#x27;re electric-line-driven mass transport boxes of some sort. If they&#x27;re not track-dependent then cost is installation and maintenance of a whole bunch of tram power lines, so cheaper than light rail but still slow to respond to population growth and change.</i><p>----<p>Buses require no tracks, no tunnels, no $5 million train cars, and a route can be switched in a day by putting up a couple new bus stop posts. Bus systems can actually be <i>profitable</i> if local governments don&#x27;t try to make political wins by drawing expensive bus routes in distant, low-volume rural areas. Buses suffer from traffic like most light rail does.<p>As an answer to urban congestion, buses are cheap, require almost no new infrastructure, can carry a ton of people, and with kinetic recovery and alternative fuel systems can be very low-impact. When used in higher density areas where personal car parking would be onerous, bus commuting can be quicker than private driving.<p>See: Lots of bus systems. Stuttgart, Germany&#x27;s SSB has hybrid buses with kinetic recovery systems improving efficiency by 18%, for example.<p>Self-driving cars or crowd-shared cars (e.g. Car2Go) provide gap-filling where bus routes don&#x27;t conveniently link up.