In NJ there are exceptions to 3 minute idling law.
<http://www.state.nj.us/dep/stopthesoot/>
1. Am I allowed to idle my diesel truck while I’m sleeping in it?
Yes, idling is allowed for heating or air-conditioning a sleeper cab while the driver or another driver is sleeping or resting in the sleeper berth in a non-residential area. An enforcement officer may need to confirm that there is someone sleeping in the sleeper berth. Drivers and trucking companies are encouraged to use alternatives to engine idling for temperature control that will save fuel and maintenance costs such as alternate power units or plug-in power available at Travel Centers of America in Paulsboro, NJ.
2. How long am I allowed to idle to warm up my diesel engine?
A motor vehicle may idle for 15 consecutive minutes when the vehicle has been stopped for 3 or more hours. However, most diesel engines take 3 minutes or less to warm up (consult the engine manufacturer’s recommendations). Limiting idling will save gas and money.