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San Francisco's Muni Aims for Zero Emissions by 2020


May 24, 2004


"Water, water, everywhere. . ." When poet Samuel Taylor Coleridge wrote those words in The Rime of the Ancient Mariner, he intended them to convey despair, but the San Francisco Municipal Railway shouts the phrase in celebration.

Muni uses water to power more than half of its 1,100 vehicles, including more than 330 of its buses.

San Francisco is supplied with hydroelectric power from Yosemite, which in turn provides the electricity for Muni's cable cars, light rail vehicles, historic streetcars, and electric trolleybuses. Furthermore, the city by the bay is surrounded on three sides by water, which means there's also plenty of unclaimed H2O for future hydrogen fuel cell buses.

Muni's recently released Zero Emissions 2020 goal targets initial fuel cell bus purchases between 2016 and 2020. Once Muni replaces its existing diesel buses with vehicles powered by fuel cells, the system will operate with 100 percent zero emissions in all five of its vehicle modes--all thanks to water. But more on that later.

First Things First

Emissions reduction is the new goal for public transportation, but it must remain secondary to the ongoing primary goal--service reliability. Muni carries an average of 737,000 riders per day on 80 routes, logging 26.6 million revenue miles per year. To ensure that system reliability does not suffer in the process of achieving zero emissions, Muni has proposed a three-part interim strategy:

* maximizing the use of zero-emission vehicles through rail and electric trolleybus expansion, as well as through a planned battery-electric bus procurement;

* expanding the use of electric-drive vehicles by replacing conventional diesel buses with hybrid-electric buses; and

* cleaning up remaining conventional diesel buses through repowers, exhaust after-treatment technology, and an investigation into the viability of alternative diesel fuels.

Zero Emission 2020 and its three-part strategy are the culmination of Muni's recently completed two-year Alternative Fuels Pilot Program, which investigated the use of hybrid-electric, compressed natural gas, liquefied natural gas, battery-electric, and exhaust after-treatment equipped buses in San Francisco's uniquely demanding transit environment.

These vehicles and technologies were evaluated for reliability and performance in a city where many sidewalks are actually steps and transit vehicles operate with crush passenger loads, as well as for cost and safety. In order to best duplicate real world conditions, the majority of Muni's AFPP data was obtained while the buses were in daily revenue service.

In addition to identifying bus technologies for future procurements, the AFPP has helped Muni to identify existing infrastructure concerns that must be addressed prior to the implementation of fuel cell buses: tunnels; low overhead contact wires; and indoor terminals.

The Role of Hybrids

The first step for Muni was choosing the most appropriate "bridge" technology for the transition from conventional buses to fuel cells.

Fuel cell buses will use hydrogen to power electric propulsion systems, so in general, there are two competency paths: experience with lighter-than-air, compressed fuels such as natural gas, and experience with electric bus technologies. Muni is fortunate to be able to take advantage of both, although one competency was certainly obtained by default. While the AFPP provided necessary insight into the operation and maintenance requirements of compressed gas fuels, Muni's 70 years of electric bus experience is already a strength.

Muni's procurement plan calls for the purchase of up to 96 hybrid-electric buses in the next few years, with additional hybrid-electric procurements to follow in the near future. Roughly 70 engine repowers and more than 400 exhaust after-treatment retrofits are also scheduled during the next few years. These plans, together with infrastructure modifications and experience with the city's fuel cell passenger cars, position Muni to be well within reach of the 2020 goal.

However, adapting to new bus technologies is not the only challenge. Muni has partnered with the San Francisco Department of Environment to create the support necessary to secure approval and funding to meet the goals presented in Zero Emissions 2020. Muni has also been working closely with city government, the California Air Resources Board, environmental groups, manufacturers, energy providers, regional planners, and other agencies throughout the industry to ensure that the plan goals are realistic and obtainable.

Water Under the Bridge

And now, back to the role of water in achieving 100 percent zero emissions, and San Francisco's plans to power fuel cell buses with water from the bay.

While Muni will likely use hydrogen reformed from existing fuel sources at the time of its initial fuel cell bus procurements, the SF Department of Environment's ultimate goal is to provide Muni with hydrogen electrolyzed using tidal power under the Golden Gate Bridge. Tidal generators would provide electricity for the city during the day, while storing hydrogen for Muni throughout the night.

So while the thirsty Ancient Mariner had "not a drop to drink," San Francisco knows there's plenty of water to power Muni and move its more than 700,000 daily passengers. Residents and riders are wiser after hearing about Zero Emissions 2020, and they overwhelmingly want this tale to go "on and on and on."

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