Nothing says paleo-futurism like an airship — in June, 1932, Science And Mechanics published this article about zeppelin cops being used to control 50,000 cars' worth of traffic. As my friend Patrick says, you can always tell alternate history novels by the zeppelins on their covers.
"Balloon Cop" Operates Stop-go Lights
In the scheme devised special traffic signals would be installed and these would be of a portable nature so that the signalling and telegraphic departments of the police could install them in a few hours. Carried up with the captive balloon would be a large cable containing the nerve centers of the entire system that would terminate in a master-control switchboard spread out before the great traffic god who by the mere manipulation of switches "would rid the traffic-burdened city of its excess vehicles in one hour, instead of the customary two or three hours now required.
This dictator would operate switches but he would also have clasped to his chest a telephone that would put him in touch with motorcycle cops at strategic points. The motorcycle cops would be immediately dispatched to points having minor accidents so that the various arteries could be kept open.