DEEP DIVE | Brief No. 006
Reading Time: 4 Minutes
Editorial Standfirst
Every journey leaves a footprint that cannot always be seen. Road transport connects cities, economies and communities, but its emissions also contribute to the air we breathe. As the world marks the International Day of Clean Air for blue skies on September 7, the question is no longer simply how to move more efficiently—but how to move while putting less pollution into the air around us.
THE INVISIBLE COST OF MOBILITY
Look at a busy road and the visible story is movement: trucks delivering goods, buses carrying commuters, cars crossing cities, motorcycles threading through traffic.
The less visible story is what accompanies that movement.
Road vehicles release nitrogen oxides, particulate matter, carbon monoxide and other pollutants. They also generate non-exhaust emissions through brake and tyre wear and road dust. In many cities, transport is a major source of nitrogen dioxide and an important contributor to particulate pollution.
The health implications are substantial. WHO estimates that ambient outdoor air pollution caused 4.2 million premature deaths worldwide in 2019, with 89% occurring in low- and middle-income countries.
The air-quality challenge, therefore, is also a mobility challenge.
WHY THIS MATTERS
- Every truck, bus, car and motorcycle is part of a much larger system.
- That system determines not only how far we travel, but also what we put into the atmosphere while travelling.
- The mobility transition will ultimately be judged by more than range, payload, charging speed or fuel economy.
- It will also be judged by something much harder to see: the quality of the air left behind.
THE ROAD TRANSPORT PARADOX
Transport remains heavily dependent on fossil energy. UNEP notes that about 95% of the world's transport energy still comes from fossil fuels. Yet the problem is not simply the number of vehicles. It is what they burn, how old they are, how well they are maintained, what standards they meet, where they operate and how intensively they are used. This becomes particularly significant with heavy-duty vehicles.
According to UNEP, heavy-duty vehicles represent only about 3.6% of the global automotive trade by value, yet they account for more than 40% of on-road NOx emissions, more than 60% of on-road PM₂.₅ emissions and more than 20% of black carbon emissions.
That is the heavy-duty paradox:
A relatively small part of the vehicle system can have a disproportionately large pollution footprint.
WHEN THE FLEET GETS OLD
The challenge becomes sharper when older vehicles move from one market to another.
UNEP has highlighted the environmental and safety implications of used heavy-duty vehicle flows, particularly where older vehicles enter markets with weaker emissions standards, fuel-quality controls or inspection regimes. Its current heavy-duty programme promotes cleaner fuels, stronger emissions standards and pathways towards electrification, particularly for buses and freight corridors in the Global South. This makes fleet renewal more than a commercial question. It becomes an air-quality intervention.
A newer vehicle meeting a higher emissions standard can fundamentally change the pollution profile of the same journey. Better maintenance can help preserve that performance. Cleaner fuels can reduce pollutant emissions. Electrification can remove tailpipe emissions altogether, although its overall environmental benefit also depends on how the electricity is generated. The transition is therefore not one technology replacing another overnight. It is a system transition.
THE CITY IS WHERE IT BECOMES PERSONAL
Air pollution becomes especially consequential where mobility and population density meet. People walking beside busy roads, commuters waiting at transport stops, drivers spending long hours in traffic and communities living alongside major freight corridors can experience greater exposure to transport-related pollutants. WHO notes that transport-related air pollution is particularly important in urban environments and around busy roadways.
This changes the question from:
How much does a vehicle emit?
to:
Who is exposed, where, for how long—and what can the mobility system do about it? That is a much broader sustainability question.
THE POLICY DIVIDE
There is no single global pathway to cleaner mobility. Some markets have progressively tightened vehicle emissions standards, fuel specifications and testing regimes. Others continue to contend with ageing fleets, limited inspection capacity and rapid growth in transport demand. UNEP's approach to heavy-duty vehicles reflects this reality: cleaner fuels and stronger emissions standards can deliver immediate reductions, while electrification and cleaner freight corridors provide longer-term pathways.
The lesson is important. Cleaner mobility is not created by the vehicle alone.
It requires an ecosystem involving:
Standards
→ What vehicles are allowed to emit.
Fuel quality
→ What goes into the engine.
Maintenance
→ How vehicles perform over time.
Fleet renewal
→ What technology remains on the road.
Infrastructure
→ What cleaner technologies can realistically operate.
Energy
→ What powers the vehicle.
Urban planning
→ How much and where vehicles need to travel.
Policy and enforcement
→ Whether the system actually delivers its intended outcome.
THE CLEANER JOURNEY
The International Day of Clean Air for blue skies was established by the UN General Assembly in 2019, with September 7 designated as the annual observance. The 2026 campaign highlights the economic as well as health case for integrated clean-air and climate action. For mobility, that message is particularly relevant. Cleaner air will not come from one fuel, one powertrain or one regulation. It will come from better choices across the entire mobility ecosystem.
Electric trucks and buses can eliminate tailpipe emissions. Cleaner combustion technologies can reduce emissions from vehicles that remain in service. Better maintenance can protect performance. Stronger standards can raise the baseline. Smarter logistics can reduce unnecessary kilometres. And integrated transport planning can reduce dependence on the most polluting forms of movement.
The destination is therefore bigger than zero-emission vehicles. It is cleaner mobility by design.
THE emBRWace PERSPECTIVE
The clean-air challenge puts the meaning of sustainable mobility into sharper focus. The question is not whether the world should continue moving. It must. The question is how intelligently it can move. A cleaner vehicle matters. A cleaner fleet matters more. A cleaner transport ecosystem matters most. The future of mobility should not only take us further. It should leave the air around the journey better.
emBRWace EXPLAINS
1.Is road transport the only cause of air pollution?
No. Air pollution has multiple sources, including energy generation, industry, agriculture, waste and household combustion. Transport is one significant contributor.
2.Are tailpipe emissions the whole problem?
No. Brake and tyre wear, road dust and other non-exhaust sources also contribute to transport-related particulate pollution.
3.Can electrification solve the problem?
It can eliminate tailpipe emissions from vehicles, but the wider environmental outcome depends on electricity generation, manufacturing, vehicle use and the broader transport system.
4.What can happen before full electrification?
Cleaner fuels, stronger emissions standards, fleet renewal, effective inspection and maintenance, and more efficient freight and public-transport systems can all contribute to cleaner air.
THE TAKEAWAY
Clean air is not separate from mobility.
It is one of the outcomes by which the mobility system of tomorrow should be measured.
Sources: United Nations Environment Programme (UNEP); World Health Organization (WHO); Climate and Clean Air Coalition (CCAC).
