I know they exist in the US from reading newsgroups a couple years back. I remember someone saying that if you fight a ticket from an automatic camera, you can demand to face your accuser. Since a camera can't give a statement in court, you will be set free. I'm sure that's just someone's assumption (stated as fact) since that seems too easy. I'm sure the human being evaluating the output of the camera and writing your ticket can be called your accuser pretty easily. Whether they would come to court or not is another issue...

I have never noticed a speed camera in use anywhere in the US. Could be there, but I haven't seen it.

The Port Authority of NY/NJ monitors your speed between two or more points if you have an EZ Pass. This information is used to estimate how long it would take you to get to another point and display it on a highway sign. For example, there is such a sign in NJ on I-80 headed toward the George Washington Bridge. It tells you how long to get to the bridge in the expess lane and how long in the local lane. I don't know if your speed info is used to issue tickets, but it certainly could be.