(a) Except as provided in subsection (b) of this section, a person may not knowingly or intentionally cause a diesel–powered motor vehicle to discharge clearly visible smoke, soot, or other exhaust emissions onto another person or motor vehicle. (b) This section does not apply to a person operating: (1) A diesel–powered vehicle that discharges visible exhaust as the result of normal acceleration or towing; (2) A commercial vehicle with a gross weight of 10,000 pounds or more; or (3) A construction vehicle operating at a construction site.
Maryland Legal Code