Are there any nationwide reporting sites in the United States?
As of now the answer is NO. You would have to report it to an agency in your City or State. Click Here for State Links There are nationwide agencies who are responsible for Traffic safety but they currently do not have a way to report unsafe driving.
National Highway Traffic Safety Administration
https://www.nhtsa.gov/about-nhtsa/contact-us
National Transportation Safety Board
https://www.ntsb.gov/Pages/home.aspx
