That's why we don't build bridges until people are swimming across, right?

Locally, my city has both a formal goal and an accompanying ordinance to reduce our greenhouse gas emissions. That would give any traffic planner or traffic engineer carte blanche to put in any infrastructure that would decrease car use. Of course, none of our traffic planners/engineers are doing anything of the sort, but they could. There's also some pretty compelling public health and economic arguments that would permit a public official to justify fewer subsidies for cars.