Urban pollution caused by traffic does not depend solely on issue vehicles: the composition of the vehicle fleet, subject , urban ventilation, and—crucially— management all have a significant impact. In addition to CO₂, major pollutants include nitrogen dioxide (NO₂), carbon monoxide (CO), and fine particulate matter (especially particles up to 2.5 micrometers or PM₂.₅), which haveserious effects on respiratory and cardiovascular health.

These particles come from both direct emissions—suchas brake and tirewear and the combustion of hydrocarbons—and the resuspension of dust accumulated on road surfaces.

Urban Congestion and Pollutant Emissions
Urban congestion occurs when traffic demand exceeds road capacity. This reduces average speed, increases travel time, and raises both emissions and fuel consumption, especially instop-and-go traffic conditions.

In situations with similar Issue , the flow of traffic determines the impact on air quality. management of vehicle traffic can reduce both overall emissions and pollution spikes, although the extent of this effect depends on factors such as the composition of the vehicle fleet, urban geometry, and weather conditions.

Intersections and Traffic Lights Intersections controlled by traffic lights often become pollution hotspots, as they concentrate traffic queues, braking, and acceleration in confined spaces.The issue stops per vehicle and speed variability are significant predictors of emissions.

In addition, repeated braking and acceleration increase particulate emissions due to brake and tire wear and contribute to the resuspension of material accumulated on the road surface. In some cases, solutions such as roundabouts or traffic calming measures—for example, textured pavement, speed bumps, or visual elements on the sides of the road—can reduce the number of stops. However,their effectiveness, ranging from 30% to 60%, depends on design and road safety conditions.

The stop-and-go traffic caused by unsynchronized traffic lights, combined with aggressive driving, canincrease emissionsby up to 60%.

This effect is particularly harmful in densely populated urban areas, where the proximity of emission sources to the exposed population increases health risks. Local concentrations of NO₂ and PM₂.₅ can rise significantly, with serious health consequences: exacerbation of asthma, worsening of chronic obstructive pulmonary disease (COPD), and increased cardiovascular risk, especially in children, older adults, and patients with pre-existing conditions.

Therefore, management should not be evaluated solely in terms of road capacity or travel time, but also in terms of its impact on the exhibition to these pollutants.

Advanced Monitoring and Smart Traffic Lights
There areadvanced systems capable of measuring pollution in real timeusing traffic cameras, environmental sensors, and pollutant dispersion models.

The accumulation of pollutants depends largely on urban morphology: the height of buildings, the presence and shape of trees and hedges, the length of streets, and their orientation relative to prevailing winds can either facilitate or hinder dispersion. As a result, certain roads and intersections are particularly susceptible to high concentrations of pollutants emitted by vehicles. Models that incorporate these factors allow for the identification of critical points where dispersion is leave where action is a priority to improve traffic flow.

These tools make it possible to identify road segments and intersections where stop-and-go driving generates significantly higher emissions than smoother traffic flow. Advanced monitoring is useful for designing mobility initiatives, adjusting traffic light cycles, prioritizing public transportation, and restricting traffic during peak times. In this way, not only is the problem identified, but action can also be taken to address the most problematic areas.

Smart traffic lights adjust wait times and traffic flow based on actual traffic demand. These systems canreduce emissions by minimizing the issue stops, smoothing out acceleration, and improving traffic flow. This also financial aid reduce fuel consumption.

The percentage improvements vary by city and subject . However, the main advantage of smart traffic lights is that they reduce instances of high-emission driving: they not only speed up traffic but alsoimprove its efficiency.

What if there are no traffic lights?
The removal of traffic lights in some urban areas, such as the city of Drachten in the Netherlands,has improved traffic flowand reduced emissions by eliminating unnecessary stops.

However, this solution is not applicable to all cities or all intersections. Its feasibility depends on factors such as traffic volume, traffic speed, road safety, and the protection of pedestrians and cyclists. Therefore, it cannot be claimed that removing traffic lights always reduces pollution. What can be argued, however, is that management tailored to the urban context—with or without traffic lights—can improve traffic flow and reduce emissions.

final, it is not just the number of vehicles on the road that matters, but also how they move. The way traffic flows directly influences emissions of CO₂, NO₂, CO, and PM₂.₅, as well as the exhibition to these pollutants. Intersections and congested corridors concentrate both emissions and the people exposed to them.

management traffic signal management can be core topic improving air quality and public health, as well as optimizing traffic efficiency.

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Enrique Baquero researcher Biodiversity and Environment Institute BIOMA) and professor at the School of Science, University of Navarra Arturo H. Ariño Full Professor Ecology, researcher Biodiversity and Environment Institute BIOMA), and research manager research Science Museum, University of Navarra   Jesús Miguel Santamaría Professor of Chemistry and Air Pollution, University of Navarra 18.05.2026