Final answer:
A vehicle not primarily designed or used to transport persons or property and only incidentally on a highway is classified as a special mobile under the Transportation Code.
Step-by-step explanation:
According to the Transportation Code, a vehicle that is not designed or used primarily to transport persons or property and that is only incidentally operated on a highway is classified as a special mobile. This class of vehicle includes a range of transportation such as non-commuting trucks and specialized vehicles that do not primarily serve the function of transporting people or goods on public roads. For instance, a commuting plug-in hybrid that predominantly operates on electric power charged at home and is rarely driven on highways could fall under this category. Such a vehicle is designed more for individual use rather than regular transportation on public roadways.