Bus fleets provide widely affordable low carbon transportation around the world. But urban buses are powered predominantly by diesel engines, accounting for approximately 25% of the black carbon emitted by the transportation sector. Future investments in low-carbon urban bus fleets should be coupled with clean fuels and soot-free engine technologies. In this way, local officials can preserve the clean air and climate benefits of their investments in urban bus fleets.
The Soot-Free Urban Bus Fleets project aims to accelerate the global transition to soot-free engine technology in the urban bus fleet. The core activity of this project is to directly inform, motivate, secure, and support the implementation of commitments made by cities to shift toward soot-free engines. This includes not only developing the soot-free commitments together with cities, but also taking the further step of making these commitments a reality – whether through advanced diesel, natural gas, hybrid-electric, electric buses or other soot-free technologies.
Due to rapidly growing urban populations and increasing demand for efficient and affordable mobility, urban bus activity is predicted to increase by nearly 50% by 2030. This will translate into an estimated additional 26,000 tonnes of black carbon emitted in 2030.
The black carbon in diesel exhaust poses a significant health risk and has been listed as a known human carcinogen by the World Health Organisation (WHO). Concentrations of black carbon are typically highest in urban areas where emission sources are most densely located. For urban residents, exposure to diesel exhaust can constitute up to 70% of their risk of exposure to air toxins.
In many countries where soot-free engines are not required by national or local laws, buses can emit more than 250 times as much black carbon as a gasoline passenger vehicle traveling the same distance. Urban buses will travel up to 10 times as much than the average passenger vehicle, increasing emissions by the same factor. Since buses can stay in service for 20 years or longer, poor emissions performance can persist for decades.