Decarbonizing bus fleets: How subnational targets can aid in phasing out combustion engines

It’s encouraging that some national governments are making commitments to shift to zero-emission transit buses. At the same time, it’s equally important to highlight that these actions have often followed earlier commitments by subnational actors at the state, provincial, and city levels. Here we define a subnational zero-emission bus target as one that prescribes that 100% of new bus sales or 100% of on-road fleets be vehicles powered by batteries or fuel cells. The table at the end of this blog is just a sample of the many subnational transit bus electrification targets around the world.

We see a strong correlation between targets and the adoption of zero-emission buses when looking at E-BUS RADAR, an online tool that tracks electric bus deployments in Latin America. It was co-developed by the Zero-Emission Bus Rapid-deployment Accelerator or ZEBRA and shows that the top two cities with the greatest number of electric buses in operation are Santiago and Bogotá. They are also cities with 100% zero-emission bus fleet targets (more details in the table). This is not a coincidence but rather evidence that adoption follows targets.

Still, not all targets are created equal. Among the various commitments made by subnational actors there is variation in the pace of transition—some are aiming for 2030, but others not until 2045. There are also differences in enforceability—some are binding laws/regulations, while others are simply announcements. All such variations have an influence on the likelihood of success, so, what distinguishes the most meaningful ones from the rest? By examining subnational targets that have already been set, we propose the following design principles for good subnational goals to shift toward 100% zero-emission bus fleets.

First, strong targets include dates for full electrification for both new bus purchases and all in-use buses (i.e., the entire on-road stock). Strong targets also have relatively more stringent timelines. The combination of total fleet coverage and a fast-tracked timeline demonstrates bold ambition and a sense of urgency, both of which are needed to fight climate change. This also sends an unmistakable signal to operators, manufacturers, infrastructure providers, and other stakeholders about the technology transition.

A case in point is our ZEBRA project in Latin America, where we dealt with a classic chicken-and-egg problem of demand and supply. Bus operators told us that zero-emission products weren’t commercially available, and manufacturers said the market demand for such products was lacking. But once municipal and state authorities articulated zero-emission transit visions, the deadlock between the manufacturers and operators was broken and they focused on transitioning away from combustion engine buses. To date, ZEBRA has secured commitments from more than 10 bus manufacturers and distributors who have agreed to make their zero-emission products available in Latin America, and investment of more than US$1 billion has been pledged from international asset owners and utility companies to help cities finance zero-emission bus technology and infrastructure. Such commitments would be hard to imagine without ZEBRA cities first having had zero-emission targets in place.

Additionally, targets need incremental steps along the way. A long-term goal alone does not create a sense of urgency. Good targets therefore spell out near-term goals and outline a gradual progression to full electrification. And it’s not just the psychology: Successful zero-emission bus procurement, operations, planning, and infrastructure development all have a learning curve. Starting with near-term milestones can allow an operator’s capacity to build up over time. For example, California has two interim points, one in 2023 (25% of new sales) and the other in 2026 (50% of new sales), and this means transit operators can gradually ramp up the share of zero-emission products in their purchases. They have until 2029 to meet the state’s 100% goal for new purchases.

It’s important for targets to stay true to technologies that generate zero tailpipe emissions. Targets should be explicit about zero tailpipe emissions, and currently the dominant technology pathways for this are battery electric and fuel cell electric. We have modeled the life-cycle greenhouse gas emissions for passenger cars, and battery electric and fuel cell electric are the only ones capable of deep decarbonization within the timeline of the Paris Agreement. We expect the same results for bus drivetrains. Ambiguous language like “low carbon” and “clean transport” are often used to promote combustion engine variants, but these won’t ultimately take us where we need to go in terms of emission reductions. Meeting climate goals means keeping the focus on zero-emission on-road vehicles, and that’s another reason why targets are important. Let’s stop making vehicles that burn stuff!

Finally, zero- and low-carbon sources of electricity and hydrogen are needed to reap the full climate benefits. Well-to-wheel emissions of battery electric and hydrogen fuel cell electric buses are lowest when powered by renewable energy. Even as the process of grid decarbonization is still unfolding, subnational entities can lead by example by procuring their own renewable energy. Some applications of this principle could include requiring a low-carbon fuel standard to manage the carbon intensity of hydrogen production, or mandating that a certain percentage of electricity be from renewable sources. For example, Seattle, which has a publicly owned electricity utility, has written in its target that the energy powering zero-emission buses in the city will need to be renewable by 2040. In South America, Santiago de Chile also requires that the electricity used to power zero-emission buses come from certified renewable sources.

Cities, provinces, and states around the world have been among the leaders in the transition to zero-emission buses. We are excited to see the target-setting principles laid out here be put into practice in the TUMI E-Bus Mission, which will set up fleet electrification targets for 20 cities in the Global South. These 20 “deep-dive cities” are meant to inspire a larger network of 500 cities and create a ripple effect that is expected to lead to procurement of more than 100,000 electric buses by 2025.


Table. Select subnational targets to reach 100% zero-emission transit buses.

Subnational entity
Asia Bangalore, India Full fleet electrification by 2030
Mumbai, India 100% electric bus fleet by 2027, with an interim 50% target by 2023
Chengdu, China 100% of new bus purchases to be zero-emission starting in 2021
Jakarta, Indonesia Transjakarta BRT fleet to become 100% zero-emission by 2030
Europe Berlin, Germany 100% zero-emission bus fleet by 2030
London, United Kingdom Entire transit bus fleet to become zero-emission by 2034
North America California, United States 100% of new purchases by transit agencies must be zero-emission buses from 2029 onward; interim targets set for 2023 and 2026; 100% zero-emission bus in-use fleets by 2040
Seattle, United States 100% zero-emission bus fleet powered by renewable energy by 2040
Washington, DC, United States 100% zero-emission bus fleet by 2045
South America Bogotá, Colombia Bogotá’s climate emergency declaration states that the city will no longer purchase transit vehicles that use fossil fuels from 2022 onward. The city aims to achieve a zero-emission bus fleet by 2035.
Cuenca, Ecuador Zero-emission bus fleet by 2035
Salvador, Brazil Zero-emission bus fleet by 2035
Santiago, Chile 100% zero-emission bus fleet by 2035
São Paulo, Brazil The São Paulo Climate Law amendment in 2018 requires the city to eliminate emissions of fossil fuel derived CO2 by January 2038. The city also has an interim goal to deploy 2,600 electric buses by 2024.
C40 Green and Healthy Streets Declaration Amsterdam, Auckland, Austin, Barcelona, Berlin, Bogotá, Cape Town, Copenhagen, Heidelberg, Jakarta, London, Los Angeles, Madrid, Medellín, Mexico City, Milan, Moscow, Oslo, Paris, Quito, Rio de Janeiro, Rome, Rotterdam, Santiago, Seattle, Seoul, Tokyo, Vancouver, Warsaw, Birmingham, Honolulu, Liverpool, Oxford, Greater Manchester, Santa Monica, West Hollywood Only procure zero-emission buses from 2025 onward


Electrification Fleets
Cities Global