A ferry service is a type of transportation service that carries passengers, vehicles, and sometimes cargo across a body of water. Ferries operate between defined ports and follow the same route on a regular schedule. They are used to transport people and goods across rivers, lakes, arms of the sea, or other bodies of water. Ferries can range from small boats carrying passengers across a harbor, lake, or river to large sea-going ships carrying passengers, cars, trucks, and other heavy cargo across longer distances where overnight sleeping accommodations are required. Ferries form a part of the public transport systems of many waterside cities and islands, allowing direct transit between points at a capital cost much lower than bridges or tunnels. They are also used as a major extension of current highway systems, especially in areas where expansion of the existing highway and bridge networks is cost-prohibitive or where building a bridge is not feasible. Ferries can be classified based on the type of cargo they carry, such as passenger ferries, car ferries, and train ferries.