Source : Grava, Sigurd 2003. “Trolleybuses.” Pp 421-436 in Urban Transportation Systems, (c) The McGraw-Hill Companies, Inc.
Types of Trolleybuses and Their Operation
Trolleybuses at this time are basically buses with a different power plant – an electric motor and power pickup poles on the roof. They are usually made by diesel bus manufacturers, adding the electrical components to a regular bus. At one time, for example, a GMC New Look bus equipped with Brown-Boveri electric components was on the market. The choices of models are limited because the market is small. Basically, standard size and articulated units are available. The external differences, beside the motor and all associated internal controls, are the two side-by-side poles that tap the power lines from below with sliding, grooved, swivelling carbon shoes.
Unlike buses, however, there is a need for rather extensive infrastructure represented by the power supply system, which has to cover the entire length of all routes as well as storage and maintenance yards. The double wires, usually placed 18.5 ft (5.6m) above the pavement, have to be held in place by insulated support cables from roadside poles or be attached to adjoining buildings. The elevation may range from 12 to 20 ft (3.7 to 6.1m). A constant elevation has to be maintained for the bottom of the power wires, which requires rather elaborate catenary arrangements. Substations are needed at regular intervals to step down the voltage to 600 to 650 dc volts. Power has to be purchased from utility companies or generated separately by the operating agency. All this represents a considerably lower capital cost than for light rail transit (no track), but is higher than for regular bus systems, even if no fuelling facilities are needed in storage and maintenance yards.
The vehicle does not have to be driven directly under the wires, but can deviate as much as 13 ft (4m) from the centre line on both sides, i.e., can move in adjoining lanes. Temporary obstacles can thus be bypassed, as long as the power poles are not blocked.