This is an accidental byproduct of an other countrywide upgrade that the government now realise they have, and are thinking up uses for.
You've probably all seen the new LED streetlights going in all over the place. Well, inside the lumiere on top of the pole, there's a lot more than a bunch of LEDs. There's a GPS transducer, light sensor, microphone and permanent data link to the control centre of the utility responsible for managing the light. The microphone was a US requirement to be able to detect and triangulate gun shot sounds to enable speedier deployment of the emergency services to a potential shooting.
Roll this forward and start thinking laterally, and you can probably come up with all sorts of uses for a connected microphone on every street corner, monitoring noisy exhausts included.