Videos of truck drivers intentionally blowing thick clouds of diesel fumes garner hundreds of thousands of views on YouTube.

It's called "rolling coal," and it occurs when a driver modifies their engine to emit a dark plume of smoke, often targeting protesters, bicyclists and even Prius drivers. 

A KGW viewer named Michael Anderson asked us to Verify: Is it legal to "roll coal" in Oregon?

Our source for this story is Deputy Brian van Kleef with Washington County Sheriff's Office. 

He says "rolling coal" is a violation of visible emission limits under ORS 815.200, and you could face a fine between $60 and $250 if you are cited.

Diesel engines are exempt from the law -- to an extent. If a regular amount of exhaust is coming out, that shouldn't be a problem. However, the moment you modify your engine, or let it build up enough fuel to intentionally blow out smoke, diesel engines are no longer exempt. 

And if that plume of smoke leads to a crash by limiting visibility, you could be held liable for the damage caused -- and face criminal charges.

"What people need to understand about light transparency, is that if you can't see at all through a plume of smoke, it's illegal under ORS 815.200," according to Washington County Sheriff's Sgt. Danny DiPietro. "My biggest concern is if there's a big plume of black smoke, it could cause a traffic crash and lead to serious injuries."  

Exemptions to the law include farm equipment and antique cars, and the law only applies to counties with populations of more than 50,000 people.  

According to the EPA's Clean Air Act, altering your emission control device is illegal. In fact, the EPA has worked with car manufacturers to make it harder for people to tamper with their car parts.

About two years ago, an Oregon man was cited for "rolling coal" at protesters during a women's march event.

And back in 2014, a truck driver got close to a group of cyclists, "rolled coal" and was eventually cited by an off duty Washington County Sheriff's deputy on a bike, Bike Portland reported. 

We can Verify: Rolling coal is illegal in Oregon and will lead to citations in counties of more than 50,000 people.

If you spot someone "rolling coal" or polluting in some other manner, you can call the Oregon Department of Environmental Quality at 1-888-997-7888 or click here to file an online complaint.  

>>Do you have something you'd like us to Verify? Email Verify@kgw.com with a selfie video of your question!