Why a trolleybus needs two overhead wires when a tram needs only one
A tram sends its electric current back through the steel rails beneath it, so one overhead wire does the job. A trolleybus runs on rubber tyres with no rail to complete the circuit, so it needs a second wire and a second pole. That simple difference shapes everything about how these electric buses work.
The first one appeared on 29 April 1882, when Ernst Werner Siemens began showing off a wire-fed carriage he called the Elektromote on the outskirts of Berlin, running trials for about six weeks. Various inventors then tried rival ways of collecting current, but the approach that won came from Max Schiemann, whose short-lived line at Bielatal near Dresden opened on 10 July 1901. His design of two parallel overhead wires, with rigid spring-loaded poles pressing up against them from below, is still the standard today.
In many places the trolleybus was first treated as a cheaper stand-in for trams. Leeds and Bradford launched Britain's first services on 20 June 1911, and Bradford also ran the country's last, closing on 26 March 1972. American systems often saw the trackless trolley as a stepping stone to streetcars, and some lines were strung up where a tram route no longer carried enough riders to justify fixing the track.
The trade-offs are real. Rubber tyres grip better than steel wheels, so trolleybuses climb hills and brake more effectively, and they are quieter than trams and can pull over to the kerb. But they carry fewer passengers, roll with more resistance, and are tied to their wires: when an explosion closed roads in downtown Vancouver in July 2008, buses had to detour several miles to stay connected. Poles can also slip off, so vehicles carry insulated ropes for drivers to hook them back on.
Around 260 systems still run in more than 40 countries. Shanghai's, opened in 1914, is the oldest still operating, and as of 2020 Kyiv had the longest network. Some cities are dropping them while others, chasing zero emissions, are building new ones, among them Marrakesh in 2017 and Prague since 2022.
Source: Trolleybus
