Examples of common types of vehicles and equipment in each of the off-road categories are found in table 6.3.1-1. More than any other source, off-road mobile sources comprises a large variety of types of different equipment and operations. An off-road inventory in any given region will typically contain about 100 types of equipment. The categories in table 6.3.1-1 are further classified into subcategories, depending on the specific equipment, fuel, size and end-use. An off-road source is defined as such only if it is portable. Therefore, items like boilers that are stationary would not be considered under this source category. However, a water pump or generator that is portable would be considered an off road mobile source.
The off-road source category is categorized into these groups (industrial, commercial, aircraft, etc.) because it is the easiest to inventory and keep track of the activities of the equipment in these categories. For example, all activity from equipment used in construction category will be related to how where and how much construction projects are occurring in a region. However, it is true that similar pieces of equipment may be found in two or more categories.