APS uses a
third rail placed between the running rails that is divided electrically into 11 m segments that automatically switch on and off according to whether a tram is passing over them, which the manufacturer states eliminates risk to other road users. Each tram has two power
collection shoes, next to which are
antennas that send
radio signals to energise the power rail segments as the tram passes over them. At any time, two consecutive segments under the tram will be live. APS is different from the
conduit current collection system, which was one of the first ways of supplying power to a tram system, as the latter involves burying a third and
fourth rail in an underground conduit or trench between the running rails. Conduit current collection was used in historic tram systems in
Washington,
Manhattan, Paris, Berlin, Marseilles, Vienna, Budapest and
London. It fell into disuse because overhead wires proved much less expensive and troublesome for street railways. APS systems boast high standards of safety and efficiency, and are minimally invasive aesthetically, which makes them especially suitable for urban settings. Overall infrastructure costs relative to catenary installation remain higher and APS systems can experience problems when operating in extremely wet and rainy conditions.
Safety Unlike the track-side third rail that is used by most
metro trains and some main-line railways, APS poses no danger to people or animals and so can be used in pedestrian areas and city streets. until as recently as December 31, 2022. == Uses ==