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Tread Wear of C3 Bus Tyres Around a City in Italy
Summary
Buses wear down their tires fast, losing over half a gram of rubber for every kilometer driven, and this worn-off rubber becomes microplastic pollution that ends up in our air, water, and soil. Since city buses are heavy and constantly stopping and starting, they may be a bigger source of this pollution than previously realized, which matters because scientists are still studying how breathing in or ingesting these tiny plastic particles affects our health. This study helps fill a data gap, giving researchers real numbers to better understand and eventually reduce tire-related pollution from public transportation.
Tyre wear is a major contributor to microplastic pollution. Heavy-duty vehicles, due to their higher weight and longer distances driven compared to passenger cars and vans, have the highest share of tyre wear from road transport. Heavy-duty vehicles cover a wide range of applications—from urban stop-and-go buses to long-distance lorries—and their maximum mass can vary from around 3.5 tonnes to more than 40 tonnes. However, experimental wear data on heavy-duty vehicles, and particularly on buses, for both original and retreaded tyres are scarce. Additionally, there is no standardised methodology for measuring their tyre wear. In this study, we measured the tread wear of regional buses operating around the city of Varese (Northern Italy) between 2019 and 2025. The tread depth reduction was 1.7–1.9 mm per 10,000 km for 22.5-inch tyres and 2.6–2.9 mm per 10,000 km for 19.5-inch tyres. Based on the annual distance driven (40,000 km for 22.5-inch tyres and 25,000 km for 19.5-inch tyres) and the tread characteristics, we estimated a mass loss of 550–800 mg/km per vehicle. These are some of the first wear emissions in the literature for new and retreaded tyres at both drive and steering axles.