Eustace introduced his bill shortly after the pickup belched soot on his Leaf. New Jersey's S2418 (full text, here) now specifically "prohibits retrofitting diesel-powered vehicles to increase particulate emissions for the purpose of 'coal rolling;' prohibits the practice of 'coal rolling.'" Those found in violation are subject to a fine by the state's Department of Environmental Protection.
Rolling coal is popular with some diesel pickup truck drivers. They can spend somewhere between several hundred to several thousand dollars on modifications that make the truck belch towers of black smoke on command, all for the apparent pleasure of leaving fellow drivers or pedestrians choking on a cloud of soot.
As NJ.com points out, the added regulation might not be entirely necessary in New Jersey. It's already illegal there for a vehicle to emit smoke for more than three seconds while driving, and rolling coal is also in violation of federal statutes. Eustace acknowledges this issue but still believes his legislation is needed. "It's to actually make sure we enforce the law. We have laws that lay fallow, I think, in some circumstances," he said to NJ.com.
A similar rolling coal bill is working its way through the Illinois General Assembly that would include a $5,000 fine for violators.