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Wireless connections: for well over a century catenary has been familiar street furniture in cities with light rail networks. But an abundance of innovative catenary-free systems is emerging that could enhance the visual impact of light rail, as Keith Barrow discovers.

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THE positioning of catenary masts and wires can sometimes be a contentious issue in cities building light rail lines, and threading power lines through environmentally-sensitive areas is often a source of intense public debate. Furthermore, power systems represent a significant proportion of the capital and maintenance costs of light rail.

The search for a viable alternative to overhead catenary dates back almost as far as the introduction of electric trams in the 19th century. The Diatto ground power supply system used studs set into the road surface, which only become live when actuated by an electromagnet mounted underneath the tram. The stud contact system was first used in 1899 in the French city of Tours, but mercury leaked from the studs making the system unreliable, and it was abandoned in favour overhead catenary in 1911. Diatto was also used in Paris, but it too was removed in 1913.

Fittingly, French cities have also been at the forefront of ground-level power supply technology in the 21st century. In 2003, Bordeaux became the first city to operate LRVs using Alstom's APS system, which has obviated the need for catenary on 13.6km of the city's 44km network. APS uses a 750V dc conductor rail embedded in the road surface, and the power supply is activated by a coded signal from the LRV as it passes overhead, meaning there is no danger of pedestrians being electrocuted. A cast...