I can envision NJ State Police checking license plates at the various bridges and pulling people over, that is what other states have done. For me it would be coming off the ferry in Cape May when they could give me 'the talk' about mandatory quarantine.
The ferry is on my travel bucket list. We tried to use it on the way home from Florida one time when I was a kid but hit traffic and missed it. It wasn’t worth waiting for the next ferry, so we just kept driving.