Rudely replying to my own post.
We don't even need to rely on the government database. Web cams in private cars feeding data to REST service at an aggregating website, maybe with a Raspberry Pi onboard to do some preprocessing....
Excuse me, I have some hacking to do.
"An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it will also make better soup." - H.L. Mencken