Final answer:
Just under one-quarter of all states have idling laws.
Step-by-step explanation:
According to the U.S. Department of Transportation, idling laws vary from state to state. While some states have comprehensive idling laws, others have more limited restrictions. However, it is safe to say that just under one-quarter of all states have idling laws. It is important to check the specific laws in each state to determine the exact regulations on idling.