Special Line Transportation refers to the business operations of road transportation companies that are established based on the needs of shippers or market cargo flows. The former primarily serves large and medium-sized industrial and commercial enterprises, with transportation companies using dedicated vehicles on fixed routes to provide shipping services to specific shippers, whether locally or in another location. This is often seen between auto parts manufacturers and assembly plants in different locations, or between auto assembly plants and remote service centers. The latter is usually set up between large and medium-sized cities and between cargo distribution centers, serving the entire society with fixed routes and schedules, mostly using large box trucks. These trucks are marked with clear identifiers such as pick-up and delivery points, phone numbers, etc. Freight rates vary with market conditions, and the density of research and development on different special lines varies. Operators of special line transportation often also provide door-to-door pick-up and delivery services. Larger-scale providers of special line transportation services often equip their operation vehicles with GPS and other tracking and monitoring systems.