Lots of factors, but I suspect at root it's just a matter of political will. Does a high enough proportion of all cities want bike bridges and do they have a re

Lots of factors, but I suspect at root it's just a matter of political will. Does a high enough proportion of all cities want bike bridges and do they have a responsive and resourced enough government to build them? I live in Boston, where commuting by bike is unfortunately still very dangerous in a lot of the city. Bike advocates are a small but vocal minority and the city has sort of responded to them, but is not moving very quickly to build out our bike infrastructure. It would take a lot more to make this happen anywhere in the ~five year frame. There's a real chicken-and-egg problem, too. Safe, pleasant bike lanes would likely do a lot to boost bike ridership while at the same time, higher rates of bike ridership are needed to "justify" their construction.