Summer use of winter tyres and the effect on fatal passenger car accidents

Mattias Hjort; Linnea Kjeldgård; Pontus Grönvall; Anders Ydenius

doi:10.55329/rsmh3109

Authors

Mattias Hjort Swedish National Road and Transport Research Institute (VTI), Sweden https://orcid.org/0000-0002-8242-3407
Linnea Kjeldgård Swedish National Road and Transport Research Institute (VTI), Sweden | Karolinska Institutet, Sweden
Pontus Grönvall Swedish Tyre Trade’s Information Council, Sweden https://orcid.org/0009-0009-7977-6592
Anders Ydenius Folksam Insurance Group, Sweden

DOI:

https://doi.org/10.55329/rsmh3109

Keywords:

braking, car crash, Electronic Stability Control (ESC), grip, induced exposure, loss of control, oversteer, traffic accident, traffic safety, tread depth, tyre type, understeer, Northern Europe

Abstract

Accidents related to insufficient road grip in Sweden have historically been investigated for winter conditions, where substantial effect on passenger car accident risk from different types of tyres has been observed. Grip-related accidents during summer conditions have so far primarily focused on the effect of Electronic Stability Control (ESC), with no assessment of possible influence from tyre properties. The use of winter tyres during summer has been increasing among passenger cars in Sweden and is currently estimated to be around 7%. Tyre tests indicate 20%–40% longer braking distances for winter tyres compared to summer tyres, and statistics have indicated that passenger cars with winter tyres are heavily overrepresented among the fatal accidents during the summer period in Sweden. The purpose of this study has therefore been to estimate the potential risk increase for a fatal grip-related accident for passenger cars using winter tyres, compared to summer tyres, during summer. Statistics from in-depth studies of fatal road accidents in Sweden from the 10-year period 2012–2021 was used in an induced exposure risk analysis, with a complementary stratified analysis investigating the effect of possible confounding factors. The results indicate that the overrepresentation among fatal accidents of cars equipped with winter tyres during the summer period to a large extent is related to the inferior road grip of winter tyres. The risk increase was particularly high for fatal grip related accidents when driving within the regulated speed limit. Tyre properties have generally been neglected as a contributing factor among fatal accidents occurring in the summer period in the Swedish in-depth studies. The present study shows that tyres have a substantial impact on grip-related fatal accidents with passenger cars in Sweden during the summer period, which account for 25% of the fatal accidents involving passenger cars. This highlights the need for increased attention to tyre properties in accident investigations. The results are most likely relevant also to other countries where winter tyres are used and the findings should be addressed by policy makers and other stakeholders.

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Author Biographies

Mattias Hjort, Swedish National Road and Transport Research Institute (VTI), Sweden

Mattias Hjort has a PhD in computational physics from Linköping University in 2001, and has been a researcher at The Swedish National Road and Transport institute (VTI) since 2003. His main research interest is vehicle technology and vehicle dynamics, with a special focus on tyres. Since 2015, he acts as research leader within the field of tyre road interaction, conducting experimental as well as theoretical studies connected to traffic safety and also environmental aspects of tyres for various vehicle types.

CRediT contribution: Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Writing – original draft.

Linnea Kjeldgård, Swedish National Road and Transport Research Institute (VTI), Sweden | Karolinska Institutet, Sweden

Linnea Kjeldgård completed her PhD in traffic safety and insurance medicine with the title ‘Sickness absence and disability pension among injured bicyclists and pedestrians’ at Karolinska Institutet. She has a broad interest in traffic safety as a researcher at the Swedish National Road and Transport Institute (VTI) since 2024. Her areas of expertise are registry research and injury statistics.

CRediT contribution: Data curation, Formal analysis, Investigation, Visualization, Writing – review & editing.

Pontus Grönvall, Swedish Tyre Trade’s Information Council, Sweden

Pontus Grönvall, MSc, received his Master's degree in Earth Sciences at the University of Gothenburg. Pontus has since the 1990-ies led the Swedish Tyre Information Council and since 2019 the Swedish Tyre Safety Council. He is responsible for numerous tyre-related studies in Sweden, including annual investigations of use of tyre type in different parts of Sweden on behalf of the Swedish Transport Administration.

CRediT contribution: Conceptualization, Data curation, Investigation, Project administration, Writing – review & editing.

Anders Ydenius, Folksam Insurance Group, Sweden

Anders Ydenius is a Senior Road Safety Researcher at Folksam. He is an expert on crash dynamics in passenger cars and its link to injuries. Ydenius joined Folksam's research department in 1995 after earning his Master's in Vehicle Engineering from KTH Royal Institute of Technology. In 2010, he completed his Ph.D. in injury prevention at the Karolinska Institutet, focusing on vehicle safety and crash injuries. Anders' expertise in vehicle safety has been applied to research-based consumer information across several areas. These include guidance on choosing safe, low-emission vehicles, safe transport vehicles for businesses, safe cars for families, selecting winter tires, and testing bicycle lights for safer cycling.

CRediT contribution: Conceptualization, Data curation, Investigation, Writing – review & editing.

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