Public transportation systems differ in the type of right-of-way each system has and the technology each system uses. These factors help determine the speed of a system, where it is able to operate, and how often vehicles in the system travel along various routes.
Right-of-way refers to the physical path that a transportation system follows. If a system has a fully controlled right-of-way, then the system does not have to yield to other transportation systems and can move more rapidly. Subways have a fully controlled right-of-way, because they run on rails dedicated solely to subway use. Therefore, subways can operate safely at high speeds. Buses must share the right-of-way with other motor vehicles on the road, and, consequently, buses move more slowly. Some rail systems, such as light rail, may have a semiexclusive right-of-way. They may share the right-of-way with motor-vehicle traffic for part of the journey, then shift to a fully controlled right-of-way, such as an elevated rail track or a tunnel, for the remainder of the trip. A fully controlled right-of-way provides the best performance of a transportation system but also costs the most money to construct. Sharing the right-of-way with other systems is cheaper, but service can suffer because of traffic or other problems.
The mechanical features of the vehicle and the riding surface of a public transportation system constitute the technology of the system. Technologies differ in cost, flexibility, and speed of travel. For instance, buses generally use diesel fuel and travel on the same streets as cars and trucks do. Rail systems may use electric motors or diesel locomotives for propulsion but are limited to traveling on steel tracks or rails. Bus technology is more flexible than rail systems, and bus routes can be easily changed to accommodate changing ridership. Rail technology is generally faster than motor-vehicle technology but is also more expensive to purchase and operate.
The most common types of public transportation are bus, paratransit, streetcar, light rail, heavy rail, commuter rail, automated guided transit, and ferry.