(en) Parker (als coördinator), Keith (2013). Transit Capacity and Quality of Service Manual. Transportation Research Board, p. 53. ISBN 9780309283441 "semi-metro — a light rail transit system that uses exclusive right-of-way for much of its length, usually at surface grade but occasionally in tunnels or on aerial structures."
(en) Organisation for Economic Co-operation and Development, Environment Committee (1973). The Automobile and the Environment, p. 10. Geraadpleegd op 9 februari 2023 "descending into tunnels in the style of conventional underground mass transit"