In 2013, there were 4,071,000 miles of roads [1]. How many cameras are we going to need? I think the idea of randomness is supposed to make people think "there could be a cop anywhere, so I'd better not speed", but I think a basic psychology education (and driving on a US highway for three minutes) proves that that's not actually how people behave.

[1] https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pu...