7. Special case: the trolleybus

Although a road vehicle, the "trolleybus" used for urban transport in many of the world's major cities uses an electrical power supply similar to that used in our study. Insulated from the road surface by its pneumatic wheels, the power supply is provided by two overhead contact wires, which are contacted by two contact wipers carried by articulated roof-mounted poles known as trolleys (figure 30 ).

The two contact wires have the same cross-section as that of a railway catenary, and the two trolleys are fitted with articulated U-shaped rubbers to enable them to rotate (figure 31 a ).