The electric trolleybus is a long established form of urban public transportation. It had a heyday in the 1930s and 1940s as replacement for street tramways. Its fortunes began to decline in the 1950s as diesels became as cost effective and the 'inflexibility' of a fixed infrastructure became to be perceived as a disadvantage. At that time, decreasing public transport ridership was often just accepted as inevitable and environmental issues were of little concern. As equipment wore out, many trolleybus systems were replaced by diesels. Falling markets for trolleybuses and their equipment increased costs and accelerated the decline.
Major oil supply crises in the 1970s reversed the process. Since then the need to improve urban public transport and increasing awareness of environmental issues have generated renewed interest in trolleybus technology. Existing systems have expanded and re-equipped and new systems opened. The announcement of a new trolleybus system for Rome and the opening of a new system in Landskrona in Sweden are examples. Rome, which already has metro and tramway systems, is investing in a 300 vehicle, 10 route trolleybus system, with off wire operation in the city's historic centre. More on:http://www.tbus.org.uk/article.htm