You're just adding another layer of abstraction. Where does policy come from? It doesn't fall from the sky like some sort of cargo cult delivery. Further, your own link highlights what I'm saying here very clearly:

"Higher funding has been made possible by burgeoning state tax receipts as aggregate incomes, spending, populations and tax rates have trended upwards. However, this close link with tax receipts has made highway funding growth responsive to economic conditions and unemployment."

So.. higher incomes, more populations, more tax receipts. Specifically, highways are a function of _human demand_. There isn't some grand conspiracy to build roads just to make a handful of companies in Michigan happy.