Rail transport (passenger) is a means of conveying passengers by moving carriages on rail tracks. Its main forms include: high-speed rail, intercity rail, commuter rail, light rail, metros, and trams. Worldwide, passenger rail travel is mostly concentrated in Asia and Europe. Since the nineteenth century the technology of rail transport has advanced dramatically. Although modern rail transport can have less environmental impact than other transport modes due to its high capacity, high speed, and clean energy source, its construction still needs careful planning because of its large investment and operating costs. In the near future, passenger rail transport will remain a major research focus in transport geography.