The progressive public health program is the first in the nation of its kind and will ensure that emissions control systems on heavy-duty vehicles operate effectively for the life of the vehicle, improving air quality and protecting public health. The HD I/M program will apply to all heavy-duty trucks, buses, agricultural equipment and personal motorhomes with a Gross Vehicle Weight Rating (GVWR) of more than 14,000 pounds travelling in the state regardless of whether they are registered in California.