Transforming transportation will be a critically important part of the decarbonization effort in the United States where the transport of people and goods produce more of the nation's greenhouse gas emissions than any other sector. Mass public transportation will be a key pillar of the green transition as it can move people around using far less energy and resources than personal vehicles-- electric or otherwise. The city of San Francisco has long recognized the many benefits of public transportation, including the use of trolleybuses for over 80 years as part of its mass transit system. 

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Trolleybuses are rubber-tired electrical transit vehicles that are powered by overhead wires rather than onboard internal combustion engines and are well suited for the steep terrian of San Francisco. In 2019, California passed the Innovative Clean Transit rule which requires the city to phase out diesel-powered transit vehicles in favor of zero-emission alternatives. Although there are several pathways to electrifying San Francisco's bus fleet, new analysis shows that protecting and expanding the city's robust trolleybus system and electrifying its diesel fleet via modern, in-motion charging (IMC) trolleybus technology can be cheaper and more resource efficient in meeting the city's climate goals.

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• Unlike traditional trolleybuses, IMC trolleybuses come equipped with onboard batteries and do not need overhead wires for their entire routes, allowing them for more flexibility in infrastructure and routes while reducing costs. A 33 percent increase in overhead wires would allow the city to double its electrified bus fleet-- adding 210 miles of electrified service.

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• IMC trolleybuses are more energy efficient that battery electric buses. They charge throughout the day via the overhead catenaries and therefore have a smoother electricity demand curve than battery electric buses.

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• IMC trolleybuses have significantly smaller batteries than battery electric buses. Reducing battery size will also reduce the need for both land to house buses in the city, and limit the materials necessary to make the batteries, like lithium.

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• The efficiencies of the IMC trolleybuses would reduce the number of transit vehicles required for service delivery by 18 percent when compared to battery electric buses and save San Francisco money as it transitions its fleet.

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• There is an existing, experienced, and robust workforce in San Francisco that already maintains and repairs an earlier generation of IMC trolleybuses. Expanding the fleet would provide long-term security for union workers as well as offer new job opportunities.

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As more transit agencies across the US begin to develop their own electrification plans, these findings have much broader implications and applications. Trolleybuses, an often-overlooked mode of transit, may hold the key to the resource-efficient, operationally simple, and economic transit systems essential to limiting the climate crisis. 

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