"They fail to mention where the GPS signals that they are using come from."
Jim, you seem to suffer from the urban myth that GPS devices transmit signals. They NEVER do, the only GPS signals or transmissions come from the satellites.
With that bit of foundation in place, the obvious answer is that the system you read about takes pictures of license plates, and uses a local GPS receiver to determine where the camera
is. Then it compares successive reports for the same license plate.
Using GPS in that application is superfluous, since the cameras are probably fixed on signposts and overheads and the position could be coded in during installation
There are other systems being deployed to count traffic and traffic speed, one is using Bluetooth signals from passing cars for the same purpose. Each BT transceiver has a unique ID, so that system just pings passing cars asking "Is there anybody there?" and recording the time and ID of every BT transmitter that passes under it. Phones, computers
, cars, whatever passes by. No camera
needed, and of course that only polls a certain percent of the traffic, but it would also work.
The common myth that GPS devices transmit a signal, the Hollywood "We put a GPS tracker on him...", is totally bogus. Trackers don't transmit a GPS signal, they forward it via a cell phone
network or other system. GPS "devices" don't transmit anything at all, except perhaps sometimes an incidental harmonic which is pretty much very short range and useless.
Imagine that, sailors...drinking and swearing like sailors. I hope no one in the USN sees "Judge Dread", they might wind
up installing the machines that automatically give you a ticket for swearing, too.
Maybe they'll start to ask what is wrong with the entire recruiting procedure, if they're recruiting folks who can't stay sober on the job. Hmmm....