Found that New York has a snitch program for enforcing their Idling laws:
$87.50 for 3 Minutes: Inside the Hot Market for Videos of Idling Trucks
I'm not going to get into whether the law itself is good or bad, because how much pollution idling trucks produce isn't something I know a lot about.
I'd assume that they idle for some the the same reasons I've left my car running in a parking lot though. Weather conditions can suck, and sometimes you don't want to run down your battery while using it for a long period of time.
But incentivizing citizens to tattle on other citizens for cash feels really scummy to me.
Diesel fuel turns into molasses in cold weather (
anything below about 32 degrees), such as you might run into in, oh, I dunno, a decent chunk of New York. Semitrucks use a heating system to ensure their fuel stays liquid but it won't work if the engine is off.
Truckers also normally sleep in their trucks, and use the engine on idle to keep the interior comfortable and to run the interior fridge, microwave, and TV (No really, there's practically an apartment in the better-equipped ones). While a 10-hour idle will burn maybe 30 bucks worth of diesel it's dramatically cheaper than a hotel even before the difficulties of parking a semi at a hotel.
The batteries make the situation even worse as the amount of power needed to start a truck is massive and a jump start alone typically runs at least a hundred bucks.
And then wear a tear, most manufacturers recommend idling for 5-10 minutes minimum to cool the engine before shutting it off, so that it cools more slowly and reduces thermal shock.