This article by wjhl.com talks about the crime-solving benefits provided by cameras installed in traffic intersections in Johnson City, Tennessee.
I have seen these same kinds of cameras also in every intersection ("every" as in everyone I drove past) in Massachusetts and Florida. Apparently there is quite a lot of monitoring going around.
These cameras are not used for traffic lights at least according to the article referenced above (which indicates that the images from the cameras are routed to some kind of monitoring center somewhere).
This question was prompted by the consideration that usually any form of tracking of citizens (and esp. of the type that invades the privacy of the citizens within their own property, although I guess being inside a car does not qualify) is supported by some law passed by Congress.
Thus the question I wanted to ask is, what law(s) has Congress passed that has allowed the installation of these cameras?