Yes it's probably hard to spend, say, $300 billion overnight on quality infrastructure projects, but it's nuts to think that there aren't numerous projects that could get going fairly quickly. You can start with my favorite, which is grants to municipalities to double the pace of their water pipe replacement. That requires no studies, no environmental impact report, no complicated engineering design, just digging up streets, replacing pipes, and repairing streets. And of course there are tons of projects that got through the study/EIR stage without ever receiving funding.
It's good stimulus, but also, you know, good policy. Repair the damn bridges.