While I recognize that roads and bridges are important, it certainly seems that Obama does consider them to be a sort of magic wand that grows the economy. I might, rather, suggest the following:
Tax policies that affect businesses
Tariff policies that affect overseas competitors and domestic exporters.
Private capital that builds factories.
Private employers determining their own wage and benefit packages and hiring to suit those packages.
You can grow the economy. You can increase wealth. You can employ people.
Roads and Bridges do not do these things in any really meaningful way.
(And I think Barry the Destroyer knows that.)
He does and so do all the pseudo-Keynesians who dominate economics in the U.S.. They believe that economic activity -- spending -- is what's important. If we all just keep our dollars circulating to the next guy, things are as good as they can get.
The idea of wealth creation, which is what happens when a farmer turns a $300 bag of seed into a corn crop worth $10,000, is unknown to them.