cars they are growing. This trend brings growing consequences for both climate and public health in cities. In the years when sport utility vehicles became widely popular, the average size of commercial vehicles kept rising. Even small cars appear to be increasing in size over time, a phenomenon that goes beyond aesthetics and enters the realm of everyday life when it comes to safety and efficiency.
Before moving forward, it is important to note that particles from wear in brakes, tires and road surfaces already account for roughly half of the pollutant particles emitted into the air from road traffic. The situation is likely to worsen as city fleets and traffic volumes rise, pushing more vehicles onto urban roads.
Brakes and tires remain notable sources of pollution.
Vehicles purchased today are larger than the ones they replace, which affects parking dynamics and raises concerns about the safety of other road users. An American study found that children were eight times more likely to be killed by an SUV than by a car, highlighting the safety gap. The Guardian reported that larger vehicles also have a greater impact on climate and air quality.
The move toward larger, heavier cars began in the 1990s. Over the past decade, European cars have grown heavier by about 9 percent on average. Small SUV sales surged fivefold while large SUV sales rose sevenfold, signaling a sustained shift in consumer preferences and vehicle weights.
Increasing vehicle weight does not only affect cars. A growing number of toxicological studies warn of possible health damages from pollution caused by brakes, road surfaces and tire wear.
An experiment shows pollution
Professor William Hicks and colleagues at Imperial College London built a computer simulator to study air pollution from brake wear. In their latest study, six different vehicles completed simulated drives around London to determine whether emissions varied significantly by vehicle type. The brakes of the large SUV model had to work twice as hard as those in the small compact car, resulting in higher particle emissions.
So what about electric vehicles? Batteries in these cars typically add about 20 percent more weight than their gasoline and diesel equivalents. Hybrid and battery-powered models, however, rely on regenerative braking, using electric motors to slow the vehicle and recover energy, which reduces friction braking and, in turn, particle emissions. Friction brakes are still used during harder, slower braking events.
In the experiment, despite the added weight, the brakes of hybrid and battery-powered vehicles operated with less pollution than their internal combustion counterparts. Brake pollution was reduced by about 88 percent in international driving tests and around 68 percent in the London tests.
Driving style also affects
Hicks explained to The Guardian that driving behavior can influence emissions from brake wear. Aggressive driving and frequent hard braking common in urban settings cause more direct wear between discs and pads and also heat brakes, leading to higher ultrafine particle emissions.
Long-term, intelligent traffic control and responsible driver attitudes should support efficient driving. In the short term, safe driving can help reduce air pollution through measures such as traffic calming, public awareness campaigns and driver education programs.
It is important to note that the effects of vehicle weight extend beyond passenger cars. Earlier London-based research linked rising heavy truck volumes to increased particle pollution from brakes, tires and road wear, underscoring the broader impact on urban air quality.
Reference work: ACS EST 2022.
Reference article: The Guardian environment report on motor vehicle obesity and air pollution, 2023.
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This topic continues to be of public policy interest and scientific investigation as cities seek to balance mobility needs with air quality and health protections.