What state is this? Typically for a lemon law, you have to do more work than just not be satisfied (Motor Vehicle Warranty and Lemon Law | State of California - Department of Justice - Kamala D. Harris Attorney General, for example).
And I wonder if it isnt time to start a separate Forum section titled "Dear Abby" or "Buyer's Remorse" where people can go to post gripes, whines, and tears. I don't mean to be a butt head, and no disrespect to Connie in particular, but I have been seeing a lot of posts where somebody is complaining and seeking advice on whether to keep the car or not. Posts like the gray carpet isn't gray enough, the lights aren't bright enough, the interior isn't quiet enough, etc., etc., etc. All asking for advice on what to do about keeping the car. Really? Stuff like this is a main forum topic? Thanks for listening to me rant. It's only been a week and a half gone of my expected 8 - 10 week wait for my car to arrive. So I am probably going to be testy for a while...
"Dear PriusChat, I just bought a Prius and love it, but then I came on here, and all I see is recent purchasers complaining about the car. I don't want to be associated with all these nutcases - can I return it?" (I'm not poking fun at the OP, mind you - just the idea of a buyer's remorse forum. It stinks that it wasn't absolutely perfect for her. Mine's been great!)
We have metal bridges in my town, and every car is noisy in them, but Prius is especially bad. But it's a tiny little bridge, so it doesn't matter. I think your problem is the special Low Rolling Resistance (LRR) tires used in Prius. These tires are hard and narrow, designed to maximize your MPG. There's a member here -- F8L -- who's an expert on this, and he might be able to make some suggestions for tires that slightly sacrifice mileage for a quieter ride, which you need. Your tires may soon be due for replacement anyway. Tirerack.com has a good article on Prius tires which discusses this. I'm not certain that new tires will solve your problem. Let's see what some experts think before you buy new tires.