Bordeaux tramway with ground-level power supply
Bordeaux tramway with ground-level power supply
CAF ACR-equipped Urbos 3 tram running through central Seville, 2015. The tram is powered by supercapacitors charged by a ground-level power supply.
CAF ACR-equipped Urbos 3 tram running through central Seville, 2015. The tram is powered by supercapacitors charged by a ground-level power supply.

Ground-level power supply, also known as surface current collection or, in French, alimentation par le sol ("feeding via the ground"), is a concept and group of technologies whereby electric vehicles collect electric power at ground level from individually-powered segments instead of the more common overhead lines. Ground-level power supply has been used primarily for aesthetic reasons. During the late 2010s it has become more economical than overhead lines.

Ground-level power supply systems date back to the beginning of electric tramways, with some of the earliest such systems using conduit current collection. Since the turn of the 21st century, new systems such as the Alstom APS, Ansaldo Tramwave, CAF ACR, Elways, and others have been introduced which use modern technology to address some of the limitations and dangers of the older systems, and supply power for buses, trucks, and electric cars. With the increased efficiency and energy density of capacitor and battery powered systems, ground-level power supply systems are used in smaller portions of the line to charge the batteries, for example only during station stops for buses and trains.

Early systems

Remaining conduit tram track on the ramp to the abandoned Kingsway tram subway in London, with plants growing in conduit
Remaining conduit tram track on the ramp to the abandoned Kingsway tram subway in London, with plants growing in conduit

Conduit current collection systems were implemented as early as 1881 with the Gross-Lichterfelde Tramway.[1]: Appendix I  The system is primarily composed of a channel, or conduit, excavated under the roadway; the conduit is positioned either between the running rails, much in the same fashion as the cable for cable cars,[2] or underneath one of the rails; a car is connected to a "plow" that runs through the conduit and delivers power from two electric rails at the sides of the conduit to the car's electric motor.[3] Plows were manually attached and detached from cars as they switched rail lines.[2]

Tram companies in Budapest trialed a conduit current collector system in 1887. Overhead lines were met with public opposition for aesthetic reasons, so the contractor Siemens-Halske implemented a concrete conduit underneath one of the trolley rails, with a narrow opening that allowed a "plow" to be inserted and make electrical contact with wires held by insulators at either side of the conduit. The system was used in several cities in Europe and the United States, where it was known as the "Budapest System". The system was generally safe, but tended to get clogged by mud and dirt. The system fell out of favor within a few years due to the cost of excavating the conduit, and was generally replaced with overhead lines.[3][4]

Stud contact systems were implemented from 1899 to 1921. Systems by the inventors Dolter and Diatto were used in Tours, Paris, and several towns in England. Power was supplied from studs set in the road at intervals, which connected to the traveling cars with contact shoes or skis. The studs were cylinders with their tops flush with the road surface. Underneath there was a switch mechanism that made an electrical connection with the top of the stud when a car with a strong electromagnet at its underside passed over it. The Diatto switches contained mercury, which often leaked or adhered to the side of the cylinder and kept the exposed top electrified. The Dolter switches used pivot arms, which tended to get stuck in the electrified position. Similar systems were operated by Thomson-Houston in Monaco from 1898 to 1903, and by František Křižík in Prague on the King Charles Bridge from 1903 to 1908.[1]: 109–116  Stud contact systems were short-lived due to safety issues.[5]

Conduit current collection systems were used in several major cities, including Monaco, Dresden, Prague, Tours, Washington, and London,[1]: 44  but posed maintenance issues and road safety issues. The Bordeaux conduit system remained the last in operation until being decommissioned in 1958. For 40 years, these systems were not reintroduced because they didn't meet modern safety standards.[5]

Modern systems

A number of ground-level power supply systems were developed from the 1970s through the 1990s,[6] but failed to reach commercialization due to reliability and safety issues.[7] The first ground-level power supply system developed to modern safety standards was the Ansaldo Stream.[5] After a competing system, Alstom APS, became the first commercially implemented system in 2003, there has been a proliferation of commercial implementations of ground-level power supply systems.[8] During the late 2010s, ground-level power supply systems have become more cost-effective than overhead line systems.[9]

Electric road systems

Electric truck driving on a public road with Elways-Evias ground-level power supply, near Arlanda airport, 2019.
Electric truck driving on a public road with Elways-Evias ground-level power supply, near Arlanda airport, 2019.

Electric roads power and charge electric vehicles while driving. Sweden has tested electric road systems that charge the batteries of trucks and electric cars, and among the tested systems are two ground-level power supply systems tested since 2017, in-road rail by Elways-Evias and on-road rail by Elonroad.[10] Both systems were found to be more economical than the tested overhead line system and dynamic inductive charging system. The in-road rail system is planned to deliver up to 800 kW per vehicle traveling over a powered segment of the rail, and the system is estimated to be the most cost-effective among the four tested systems. The new systems are expected to be safe, with segments of the rail being powered only when a vehicle is traveling over them.[11] The rails have been tested while submerged in salt water and were found to be safe for pedestrians.[12] The co-director for one of the French Ministry of Ecology working groups on electric road systems stated that rail-based ERS are the most advantageous, though the specific rail technology has yet to be standardized.[13]


Alstom, Elonroad, and other companies have, in 2020, begun drafting a standard for ground-level power supply electric roads.[14][15] The European Commission published in 2021 a request for regulation and standardization of electric road systems.[16] Shortly afterward, a working group of the French Ministry of Ecology recommended adopting a European electric road standard formulated with Sweden, Germany, Italy, the Netherlands, Spain, Poland, and others.[17] The standard, CENELEC Technical Standard 50717, is scheduled to be approved and published by November 14, 2022.[18]

Modern implementations

Ansaldo Stream

The first modern ground-level power supply system to be developed is the Ansaldo Stream system. STREAM is an acronym that stands for "Sistema di TRasporto Elettrico ad Attrazione Magnetica", meaning "System of Electric Transport by Magnetic Attraction". The system uses a channel in the road made of insulating composite fiberglass material which contains a flexible copper strip; a vehicle passing over the channel with a special magnetic contact shoe raises the conductor to the surface, allowing power to flow to the vehicle. Segments of the strip are powered only when a vehicle passes over them. The system was developed in 1994[19] and trialed on a public tram line in 1998,[5] which was eventually dismantled in 2012.[20]

Alstom APS

A section of APS track showing the neutral sections at the end of the powered segments plus one of the insulating joint boxes which mechanically and electrically join the APS rail segments
A section of APS track showing the neutral sections at the end of the powered segments plus one of the insulating joint boxes which mechanically and electrically join the APS rail segments

Alstom APS uses a third rail placed between the running rails, divided electrically into 11-metre segments. These segments automatically switch on and off according to whether a tram is passing over them, thereby eradicating any risk to other road users. APS was developed by Innorail, a subsidiary of Spie Enertrans but was sold to Alstom when Spie was acquired by Amec. It was originally created for the Bordeaux tramway, which was constructed from 2000 and opened in 2003, becoming the first modern commercial ground-level power supply system. From 2011, the technology has been used in a number of other cities around the world.[21][22] Alstom further developed the system for use with buses and other vehicles.[23]


Construcciones y Auxiliar de Ferrocarriles (CAF) trialed its Acumulador de Carga Rápida (ACR) ground-level power supply system in 2007 in Seville. Sections of the Seville MetroCentro tramway around the Seville Cathedral were converted to the ACR ground-level power supply system. ACR’s first commercial installation was aboard Urbos trams supplied to MetroCentro in 2011, allowing the permanent removal of overhead lines around the cathedral.[24]

Line 1 of the Tranvía de Zaragoza has also used ACR since its second construction phase was completed in 2013. The use of ACR avoided the installation of overhead lines in the city’s historic centre.[25][26]

ACR was included in the Newcastle Light Rail in Australia and Luxembourg's new tram system.[27][28]

Ansaldo Tramwave

Derived from Ansaldo Stream and developed by Italian company Ansaldo STS (which later became Hitachi Rail STS), the Ansaldo TramWave ground-level power supply system successfully entered commercial application in 2017, with the opening of Zhuhai tram Line 1 first phase in China. The tram is the first fully low-floor tram system adopting ground level power supply technology.[29] Later in 2017, Western Suburb Line in Beijing was opened with the same technology from Ansaldo.[30] The technology has been licensed to CRRC Dalian and all the technologies were transferred to China.[31]


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  2. ^ a b Dewi Williams (2004), London Trams: current collectors (ploughs)
  3. ^ a b Eric Schatzberg‬ (2001), Culture and Technology in the City: Opposition to Mechanized Street Transportation in Late-Nineteenth-Century America, MIT Press
  4. ^ Legát, Tibor; Zsolt L. Nagy; Gábor Zsigmond (2010). "Bevezető [Introduction]". Számos villamos [Numbered tram] (in Hungarian). Budapest: Jószöveg. pp. 6–12. ISBN 978-615-5009-15-0.
  5. ^ a b c d J Baggs (March 9, 2006), "5.1 Ground Level Power Supply", Wire-Free Traction System Technology Review (PDF), Edinburgh Tram Network
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  7. ^ Michael P. Hennessey (January 1994), Evaluation of the E-TRAN Vehicle Propulsion Concept (PDF), Minnesota Department of Transportation, pp. 11–12
  8. ^ John D. Swanson (April 7, 2019), "Continued Advances in Light Rail / Streetcar Vehicle Off-Wire Technology" (PDF), Transportation Research Board
  9. ^ Guerrieri, M. (2019), "Catenary-Free Tramway Systems: Functional and Cost–Benefit Analysis for a Metropolitan Area.", Urban Rail Transit (5): 289–309, doi:10.1007/s40864-019-00118-y
  10. ^ D Bateman; et al. (October 8, 2018), Electric Road Systems: a solution for the future (PDF), TRL, pp. 146–149
  11. ^ Analysera förutsättningar och planera för en utbyggnad av elvägar, Swedish Transport Administration, February 2, 2021, pp. 21–23, 25–26, 54
  12. ^ Daniel Boffey (April 12, 2018), "World's first electrified road for charging vehicles opens in Sweden", The Guardian
  13. ^ Laurent Miguet (April 28, 2022), "Sur les routes de la mobilité électrique", Le Moniteur
  14. ^ PIARC (February 17, 2021), Electric Road Systems - PIARC Online Discussion, 34 minutes 34 seconds, 2 hours 36 minutes 51 seconds, archived from the original on 2021-12-22
  15. ^ Martin G. H. Gustavsson, ed. (March 26, 2021), "Key Messages on Electric Roads - Executive Summary from the CollERS Project" (PDF), CollERS, p. 6, retrieved February 11, 2022
  16. ^ European Commission (July 14, 2021), Proposal for a REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on the deployment of alternative fuels infrastructure, and repealing Directive 2014/94/EU of the European Parliament and of the Council
  17. ^ Patrick Pélata; et al. (July 2021), Système de route électrique. Groupe de travail n°1 (PDF), archived from the original (PDF) on October 2, 2021
  18. ^ "PD CLC/TS 50717 Technical Requirements for Current Collectors for ground-level feeding system on road vehicles in operation", The British Standards Institution, 2022, archived from the original on April 23, 2022, retrieved April 23, 2022
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  20. ^ "Partono i Lavori per la Rimozione delle Rotaie di Stream in via Mazzini", TriestePrima, 16 February 2012
  21. ^ "Third-rail trams across the Garonne". Railway Gazette International. 2004-02-01. Retrieved 2008-05-02.
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  26. ^ Crespo Roig, María (2011-01-20). "CAF apuesta por que Zaragoza tenga un metro sin catenarias que funcione con la energía que recargue en las paradas". (in Spanish). Zaragoza. Retrieved 2018-07-16.
  27. ^ "Newcastle light rail to be Australia's first 'wire-free' system". 19 April 2017.
  28. ^ "Newcastle Light Rail, Australia | Aurecon".
  29. ^ 历经磨难 全球首个地面供电的100%低地板现代有轨电车项目终成正果
  30. ^ 去颐和园、香山更方便啦!西郊线年底运营,还能和地铁换乘
  31. ^ 中国首次引进现代有轨电车技术(图)