Maryland has banned the practice of “rolling coal” in which drivers of diesel pickup trucks intentionally spew black exhaust at pedestrians, cyclists and other motorists.
Yes, it’s a thing. The Internet abounds with videos.
As of Oct. 1, motorists who intentionally blow visible exhaust at a person or vehicle can be fined up to $500. Rolling coal is done to attack protesters, show disdain for “foreign” or hybrid vehicles, or, apparently, as a dirty prank, according to the videos. Maryland Gov. Larry Hogan (R) signed the bill Thursday.
More:
https://www.washingtonpost.com/news/dr-gridlock/wp/2017/05/26/no-more-rolling-coal-on-maryland-roads/