The highest capacity types of transit include steel wheel on steel rail systems such as:

Commuter rail, usually running on shared freight lines and pulled by diesel locomotives;
Urban subway powered by third rail;
Urban and suburban light rail powered by overhead catenary; and
Suburban rail powered by on-board diesel engines.

These systems generally have high speed and high capacity which can require considerable capital investment. These systems usually occupy independent corridors, but sometimes may be designed in public roadway corridors.

At the other end of transit are traditional highcapacity buses and smaller passenger vans (also referred to as microtransit) that use public roadways and are mixed into the general-purpose traffic. These often run on local and rural roads. In general, bicycle, pedestrian, and micromobility devices fill the need for first mile/last mile connections completing a transit trip. Additionally, some buses can be configured for express between two points and travel freeways, toll roads, or managed lanes. These often require minimal capital investment other than the buses, bus maintenance facilities, and furniture for bus stops.

In-between rail and buses are new innovative transit approaches such as Bus Rapid Transit (BRT). This combines the low capital cost of existing roadway assets with the efficiency and capacity of dedicated transitways. This approach was pioneered in Curitaba, Brazil as early as 1974 and included dedicated roadway for the bus vehicles, level boarding with wide doors, pre-payment at loading platforms, and articulated buses. BRT quality is ranked by the Institute for Transportation & Development Policy (ITDP) and includes criteria for engineering, planning, operations, stations, communications, and access. Full BRT systems that essentially operate as traditional rail transit are given higher scores while “BRT-light” systems that only incorporate portions of the BRT concept are given lower scores.

As technology improves, newer types of public transit may emerge. Examples might be ondemand transit using autonomous vehicles, EV transit vehicles, point-to-point autonomous vehicles designed for one or two passengers, driverless smaller vehicles on dedicated transitways with more frequent service, etc.