Public Investment is never just for public benefit

A lot of public investment (especially in new infrastructure) is targeted toward eliciting private investment. Sometimes the degree and share of subsidy is more obvious, sometimes the ROI is more dubious. Public sector would be better off addressing what it controls directly (the regulation-imposed costs on new development) rather than attempting to allocate capital.  

Lot of transportation planning is about providing mobility--enabling people to get between places faster. A much smaller share of it is about providing access--making it possible to get 'there' at all. Partially, that reflects the maturity of the US highway network--where goes pretty much anywhere you want to go. But accessibility takes a front seat when we talk about our much-less-mature networks of walking, cycling, or transit.