Let The Sparks Fly

 

The trackless trolley coach is an electric vehicle, a development of streetcar technology. They gained more acceptance by the late 1930s in large metropolitan cities across North America and became a common sight by the 1950s, with some soldiering on well into the 1960s.

By using much of the existing electrical propulsion system and distribution infrastructure already in place for streetcars, it was a cost-effective expansion of the transit system, requiring no investment in rails. Each coach appeared as the traditional rubber-tired transit bus, thus needing a second overhead wire as an electrical ground. Trackless coaches drew their electricity by utilizing the bus's two trolley poles (power collectors) attached to overhead wires. At certain points along the route, one could hear the cracking of sparks as the trolly poles came in contact when crossing parallel overhead lines or when making turns. 

Note: Chicago's trackless coach service (1964 image above) ended in 1973, co-existing with engine-powered buses that could shuttle passengers beyond the inner city. A few European cities still use this system, with Boston being the only US city as of early 2022.