What&#x27;s practical and what&#x27;s cost effective aren&#x27;t necessarily the same. Subways or really most any commuter train is only close to cost effective in some of the more extreme urban densities, and it is real energy hog if people aren&#x27;t using it. It would likely make sense to build more subways, but there are a handful of spots in the US where it could be a solution at all.<p>Options like buses and shared vans&#x2F;cars are no one&#x27;s preferred ride, but it is an infrastructure that&#x27;s already scaled up for all of the US, and it ends up being very cheap. It takes less traffic reduction than you might think to make congested roads fast moving.<p>It is also worth pointing out that SF essentially is building the infrastructure to replace the BART with buses right now...Buses from the new terminal will have a dedicated ramp on to the bay bridge, and I wouldn&#x27;t be surprised if they end up getting a full lane for the full BRT experience. If you haven&#x27;t noticed an impact from that construction, versus say the Chinatown subway messing up all of 4th street, then it really speaks to why buses are a pretty easy solution.