Zero-emission HD fleets

May 6, 2016
Santa Monica bus fleet: an early adopter case study

Santa Monica’s Big Blue Bus (BBB), an iconic fleet of 200 transit buses operated by the City of Santa Monica, has been a leader in adopting natural gas as an alternative fuel to diesel since 2014. Serving one of the most traffic-congested regions in the nation, Big Blue Bus continually strives to improve its impact on the environment while conscious of budget constraints.

BBB became one of the country’s first municipal transit authorities to convert its fleet to renewable natural gas (RNG) when it made the switch to gas captured from landfills in 2015. The use of captured landfill gas as RNG reduces the BBB’s carbon footprint by a staggering 90%.

Greenhouse gas reduction has always been a big part of the City’s strategy. Prior to 2015, BBB’s use of conventional LNG reduced greenhouse gas (GHG) emissions by over 2,000 metric tons per year.

However, City officials were looking for a non-fracked alternative fuel that the public could get excited about and partnered with Clean Energy to bring renewable natural gas to their refueling stations. When considering RNG, the City estimates GHG reduction at over 9,000 metric tons when compared to a baseline of diesel. That’s the equivalent of taking nearly 2,000 cars off the road per year.

In the pursuit to use the lowest emission vehicle commercially available, and to maximize the benefits of using RNG, the transit agency has committed to retiring 25 natural gas buses (model years 2002 and 2004) and replacing them with new vehicles supplied by Gillig and equipped with Cummins Westport’s ISL G near-zero (NZ) NOx natural gas engine. This NZ engine reduces smog-forming NOx emissions by 95% compared to even today’s most stringent on-road diesel regulations. On an annual basis, tailpipe NOx emissions from a full heavy-duty vehicle powered by this engine are a few dozen pounds—comparable to the emissions output of a midsize gasoline-powered automobile driving far fewer miles.

In addition to these first 25 newly manufactured coaches, BBB will also repower 30 buses with the ISL G NZ engine, bringing the total number of ultra-clean engines in their fleet to 55. The result of pairing low-carbon RNG with the near-zero NOx engine will create the cleanest heavy-duty transit fleet in the U.S.

Once deployed and fueled with RNG, the BBB fleet with the ultra-clean natural gas engine will deliver emission reductions that are at least as good and possibly better than comparable battery-electric heavy-duty vehicles. As a first mover on this ultra-low emission engine and fuel combination, BBB is demonstrating how a large heavy-duty vehicle fleet that must complete a full day of rigorous work can also achieve comparable environmental performance to what is traditionally considered a zero-emissions vehicle. BBB is showing that this can be done at scale with today’s technologies and fuels and at a cost that is no more than its current operations.

As progressive corporations across America look for ways to reduce their costs and environmental footprint, there is no doubt that others will begin to follow BBB’s lead. Trucking companies looking to differentiate themselves from their competition have an unprecedented opportunity to show their customers that they can deliver the goods effectively and emission-free. Likewise, shippers looking to have their products hauled via trucks with a minimal environmental footprint will see the tremendous value and opportunity from this engine/fuel combination. 

About the Author

Erik Neandross | Contributing editor

Erik Neandross is CEO of Gladstein, Neandross & Associates (GNA), the clean transportation and energy consulting firm that organizes the Alternative Clean Transportation (ACT) Expo. Learn more at and

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