Sustainable Transport

C40 Cities
6 min readSep 3, 2021

How are cities using sustainable transport to clean our air?

Credit: C40 Cities

The United Nations’ International Day of Clean Air for blue skies highlights a fundamental human right that so many people are denied — the right to breathe clean air.

Around nine in ten people around the world breathe dirty air every day, which not only leads to avoidable health issues and premature deaths, but also disproportionately affects the most vulnerable and marginalised communities.

We know that air pollution and the climate crisis go hand-in-hand. Both need swift, unprecedented and collective action to protect our health and prevent the catastrophic warming of our planet.

Instead of waiting for others to take action, mayors from 37 global cities have come together to make air pollution a thing of the past by committing to the C40 Clean Air Cities Declaration. Signatory cities have pledged to a range of commitments, including ambitious reduction targets for pollutants and the implementation of substantive new policies and programmes to clean the air we breathe.

Here is how mayors of world-leading cities are acting to protect residents from the devastating consequences of air pollution.

In Bogotá, the capital city of Colombia, transport is accountable for 70% of the city’s air pollution generated by combustion sources. However, as a signatory to both the Green and Healthy Streets and Clean Air Cities Declarations, Mayor Claudia López is working towards reducing emissions and improving air quality for people and the planet.

“Bogotá has committed to strengthening our zero and low-emission technologies in urban transportation, as well as fuel improvements. This pledge is a cornerstone in addressing Bogotá’s major environmental challenge: improving air quality.

“We are working to advance our understanding of specific micro-environments and design cross-sectorial policies for better air quality. Behavioural change, earnest commitment from the public and private sector, and co-responsibility from all stakeholders are fundamental for Bogotá to meet PM 2.5 (17%) and PM 10 (14%) concentration reduction targets by 2030.” — Mayor of Bogotá, Claudia López.

As of August 2021, Bogotá already has an operating fleet of 483 zero-emission buses that carry around more than 100,000 residents every day, as well as four re-charging depots. These numbers are just the start — the city’s recent tenders with Transmilenio S.A., the transport authority of Bogotá, awarded 1,002 additional electric buses that will be deployed by mid-2022. In addition to providing clean transport, the city is outlawing the procurement of fossil-fuelled buses starting in 2022, as a result of their Climate Emergency Act.

The city of Guadalajara, Mexico is also championing sustainable mass transit. A fleet of 38 new electric buses have been deployed in the city, mostly operated by women drivers, to form part of the country’s first electric transport corridor. The 28-kilometre route will carry about 23,000 passengers per day, benefiting low-income neighbourhoods within the city — creating positive health and social outcomes.

Durban (eThekwini) holds sustainability as the overarching philosophy that guides the city’s transport planning. The eThekwini Transport Authority is currently improving its fleet of GO!Durban buses and finding alternatives to the combustion engines normally used in the fleet. The city’s main goal is to increase the use of public transportation as well as promoting non-motorised transport, while integrating these objectives into city planning. The city is working with C40 to plan and develop a Low Emission Zone Concept that is due to be implemented by 2030.

The Italian city of Milan is surrounded by mountains, making it more difficult for pollution to disperse. After recording dramatically cleaner air during its lockdown at the beginning of the Covid-19 pandemic in 2020, the city is working towards preserving these changes in air quality, as well as implementing actions to further clean the air.

In April 2020, Milan’s ‘Strade Aperte’ programme initially transformed 22 miles (35 km) of roads. This rapid, experimental scheme, designed to both protect residents from Covid-19 and reduce car use, included temporary cycle lanes, widened pavements, low speed limits, and priority streets for residents to walk and cycle. The success of this programme saw it expand to 42 miles (68 km).

The capital of Peru, Lima worked with the C40 Benefits Analysis team on two projects. The first, approved in 2015, banned cars from 68 blocks within the historical city centre on every Sunday from 9am to 5pm — creating 15 kilometres of public space that prioritises walkers and cyclists. Lima is building on the success of this scheme with another push towards improving air quality with the pedestrianisation of 41 blocks in the historical city centre.

To confront air pollution in England’s capital, Mayor of London Sadiq Khan rolled out the Ultra Low Emission Zone (ULEZ). It is the world’s strictest Low Emission Zone, and it operates 24/7, every day of the year.

Since it was announced in 2017, the city has seen 44,100 fewer polluting cars on the road each day, contributing to a 44% drop in roadside nitrogen dioxide ( NO₂) in the central London ULEZ (based on pre-pandemic data). Many Londoners are experiencing a major change in the quality of their air, with a 94% plummet in the number of people living in areas exceeding legal limits for NO₂ between 2016 and 2019. Likewise, 97% of primary and secondary schools are seeing the same benefit — schools in areas with illegal levels of air pollution went from 455 schools in 2016, to just 14 in 2019. But air pollution is not just a central London problem, which is why the Mayor is expanding the ULEZ to an area 18 times larger than the central zone from October 2021.

“I pledge to be the greenest Mayor London’s ever had with a mandate from Londoners to put the environment and climate policies at the heart of my second term in office.

“In central London, the Ultra Low Emission Zone has already helped cut toxic roadside nitrogen dioxide pollution by nearly half and led to reductions that are five times greater than the national average. But pollution isn’t just a central London problem, which is why expanding the ULEZ later this year will benefit Londoners across the whole of the city and is a crucial step in London’s green recovery. There is no time to waste. We know pollution hits the poorest Londoners the hardest which is why I’m doing everything I can to improve the health for all Londoners.” — Mayor of London, Sadiq Khan.

The air in Sydney, Australia’s most populated city, has been affected by bushfires, dust storms and heatwaves, making it even more important for emissions from transport to be kept as low as possible. The first electric bus was introduced in the city in February 2021, with the aim of introducing 50 more by the end of this year. Eventually, the goal is to ensure Sydney’s entire fleet is electric. As well as protecting the health of residents, Sydney is becoming more sustainable and resilient through its Environmental Action Strategy (2021–2025).

Mayors are also taking steps to protect the health and well-being of residents by giving public space back to people and nature, reclaiming our streets to create liveable local communities. As part of their Agenda for a Green and Just Recovery, mayors are creating ‘15-minute cities’ where all residents are able to meet most of their needs within a short walk or bicycle ride from their homes. By implementing the 15-minute city concept, residents become better connected to their jobs, schools, leisure, and their loved ones, while air quality is improved by facilitating shorter trips and sustainable transport options. Across the C40 network mayors are implementing policies that incentivise walking and cycling, expand public transport and through zero emission zones, encourage people to leave their polluting vehicles behind.

These initiatives reflect the bold actions that signatories are taking in their pursuit of reducing damaging pollutants. The 37 signatories are not only providing cleaner, healthier air for residents and protecting the health and livelihoods of millions of people across the world, but are also adopting sustainable solutions that can help in the fight against the climate crisis and enable a just transition.

By working together to meet the commitments of the C40 Clean Air Cities declaration, we can secure a future where everyone, everywhere can breathe clean air.



C40 Cities

C40 is a leading global network of cities taking bold and ambitious climate action to deliver a healthy, equitable and sustainable future for all.