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. This section does not apply to a person operating: A diesel–powered vehicle that discharges visible exhaust as the result of normal acceleration or towing; A commercial vehicle with a gross weight of 10,000 pounds or more; or A construction vehicle operating at a construction site.