As with tolling and public-private partnerships, idling laws which restrict the duration of time a trucker can idle his/her truck while resting in the truck cab complying with Hours of Service regulations (HOS), loading and unloading, etc. has also come down to a patchwork of various local and state regulations.
As a trucker travels from one end of the country to the other he/she oftentimes does not know the idling laws in each locality, and oftentimes is awakened in the middle of the night with a knock on the window by law enforcement asking to turn off their truck, and sometimes fining the driver. In fact, in some cases state and local regulations protect animals left in vehicles more than truckers trying to rest in the cab of their trucks.