Omitted (probably not even considered):

Free public transit

(seriously, click the link, the video is pretty cool ... but it's probably more of a state/federal project in the end.)

A mass transit system that gets most of its operating and construction budget from taxes, as opposed to fares, can easily improve the return(in passenger miles per tax dollar spent) on those taxes if reducing the fares to zero improves ridership dramatically. Especially if the primary object is to discourage car ownership / ridership.