IDEAS home Printed from https://ideas.repec.org/a/eee/trapol/v178y2026ics0967070x25005128.html

Slower roads, cleaner skies? causal effects of speed limit reduction on urban air quality using propensity score matching and spatial difference-in-differences regression

Author

Listed:
  • Yang, Wookjae
  • Kang, Byunguk

Abstract

Vehicle speed limit reduction policies have been widely studied for their impact on traffic safety outcomes, such as reducing crash frequency and severity. However, little attention has been paid to the effects on air quality that may have resulted from traffic volume changes induced by speed reductions. This study aims to assess the causal impact of the speed limit reduction policy in the Republic of Korea, “5030 Speed Limit Reduction"- urban roads from 60 to 80 km/h to 50–60 km/h and on local roads from 40 to 60 km/h to 30 km/h, on air quality, explicitly targeting particulate matter (PM10), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs). By employing a quasi-experimental study design that combines propensity score matching (PSM) and spatial difference-in-differences (SDID) regression, this research addresses gaps in existing studies by investigating the causal impact of speed limit reductions on air quality and spatial dependence, while controlling for confounding variables, such as built environment and socioeconomic status. The PSM result indicates that after matching, the mean differences between the treatment and control groups were substantially reduced, indicating that matching effectively balanced covariates. The results of three different difference-in-difference models (linear regression DID, spatial error DID, and spatial lag DID) were applied to five air pollutants: CO2, CO, NOx, VOCs, and PM10. The treatment effect is positive and statistically significant across all pollutants, except NOx. This confirms that the speed limit reduction policy increased traffic volume and, consequently, increased emissions, thereby worsening air quality. Although the policy successfully contributes to the United Nations' Sustainable Development Goals (SDGs) by significantly reducing crashes and enhancing road safety, it falls short of achieving another key aspect of sustainability, improving air quality. Therefore, comprehensive strategies are required to achieve sustainable urban environments.

Suggested Citation

  • Yang, Wookjae & Kang, Byunguk, 2026. "Slower roads, cleaner skies? causal effects of speed limit reduction on urban air quality using propensity score matching and spatial difference-in-differences regression," Transport Policy, Elsevier, vol. 178(C).
    • Handle: RePEc:eee:trapol:v:178:y:2026:i:c:s0967070x25005128
    DOI: 10.1016/j.tranpol.2025.103969
    as

    Download full text from publisher

    File URL: http://www.sciencedirect.com/science/article/pii/S0967070X25005128
    Download Restriction: Full text for ScienceDirect subscribers only
    File URL: https://libkey.io/10.1016/j.tranpol.2025.103969?utm_source=ideas
    LibKey link: if access is restricted and if your library uses this service, LibKey will redirect you to where you can use your library subscription to access this item
    ---><---

    As the access to this document is restricted, you may want to

    for a different version of it.

    References listed on IDEAS

    as
    1. Yang, Wookjae & Chang, Justin S., 2025. "A quasi-experimental study of light rail transit on jobs-housing balance by regional typology: A case study of South Korea," Journal of Transport Geography, Elsevier, vol. 124(C).
    2. Stephen Kome Fondzenyuy & Blair Matthew Turner & Alina Florentina Burlacu & Chris Jurewicz & Davide Shingo Usami & Steffel Ludivin Tezong Feudjio & Luca Persia, 2024. "The Impact of Speed Limit Change on Emissions: A Systematic Review of Literature," Sustainability, MDPI, vol. 16(17), pages 1-17, September.
    3. van Benthem, Arthur, 2015. "What is the optimal speed limit on freeways?," Journal of Public Economics, Elsevier, vol. 124(C), pages 44-62.
    4. Lisa Schweitzer & Jiangping Zhou, 2010. "Neighborhood Air Quality, Respiratory Health, and Vulnerable Populations in Compact and Sprawled Regions," Journal of the American Planning Association, Taylor & Francis Journals, vol. 76(3), pages 363-371.
    5. Megan Heckert & Jeremy Mennis, 2012. "The Economic Impact of Greening Urban Vacant Land: A Spatial Difference-In-Differences Analysis," Environment and Planning A, , vol. 44(12), pages 3010-3027, December.
    6. Int Panis, L. & Beckx, C. & Broekx, S. & De Vlieger, I. & Schrooten, L. & Degraeuwe, B. & Pelkmans, L., 2011. "PM, NOx and CO2 emission reductions from speed management policies in Europe," Transport Policy, Elsevier, vol. 18(1), pages 32-37, January.
    7. Zhai, Guocong & Xie, Kun & Yang, Di & Yang, Hong, 2022. "Assessing the safety effectiveness of citywide speed limit reduction: A causal inference approach integrating propensity score matching and spatial difference-in-differences," Transportation Research Part A: Policy and Practice, Elsevier, vol. 157(C), pages 94-106.
    8. Dubé, Jean & Legros, Diègo & Thériault, Marius & Des Rosiers, François, 2014. "A spatial Difference-in-Differences estimator to evaluate the effect of change in public mass transit systems on house prices," Transportation Research Part B: Methodological, Elsevier, vol. 64(C), pages 24-40.
    9. Riccardo Rossi & Riccardo Ceccato & Massimiliano Gastaldi, 2020. "Effect of Road Traffic on Air Pollution. Experimental Evidence from COVID-19 Lockdown," Sustainability, MDPI, vol. 12(21), pages 1-17, October.
    10. Jucheol Moon & Jin Gi Hong & Tae-Won Park, 2022. "A Novel Method for Traffic Estimation and Air Quality Assessment in California," Sustainability, MDPI, vol. 14(15), pages 1-12, July.
    Full references (including those not matched with items on IDEAS)

    Most related items

    These are the items that most often cite the same works as this one and are cited by the same works as this one.
    1. Filipi Nikol & Karlínová Bára & Krčál Ondřej, 2022. "The disutility of driving below the speed limit on highways," Review of Economic Perspectives, Sciendo, vol. 22(4), pages 267-277, December.
    2. Fang Wang & Yaoyao Peng & Chunyan Jiang, 2017. "Influence of Road Patterns on PM 2.5 Concentrations and the Available Solutions: The Case of Beijing City, China," Sustainability, MDPI, vol. 9(2), pages 1-17, February.
    3. Hu, Songhua & Orsi, Giacomo & Santi, Paolo & Wang, An & Fugiglando, Umberto & Ratti, Carlo, 2025. "Evaluating the impact of zone 30 policies on citywide road traffic emissions and efficiency: A big data-driven approach," Transportation Research Part A: Policy and Practice, Elsevier, vol. 202(C).
    4. Andre Chagas & Carlos Azzoni & Alexandre Almeida, 2015. "A Spatial Difference-in-Difference Analysis to Measure the Sugarcane Producing Impact in Respiratory Health," ERSA conference papers ersa15p511, European Regional Science Association.
    5. Sunak, Yasin & Madlener, Reinhard, 2016. "The impact of wind farm visibility on property values: A spatial difference-in-differences analysis," Energy Economics, Elsevier, vol. 55(C), pages 79-91.
    6. Stephen Kome Fondzenyuy & Blair Matthew Turner & Alina Florentina Burlacu & Chris Jurewicz & Davide Shingo Usami & Steffel Ludivin Tezong Feudjio & Luca Persia, 2024. "The Impact of Speed Limit Change on Emissions: A Systematic Review of Literature," Sustainability, MDPI, vol. 16(17), pages 1-17, September.
    7. Chávez, Alicia & Rodríguez-Puello, Gabriel, 2022. "Commodity price shocks and the gender wage gap: Evidence from the Metal Mining Prices Super-Cycle in Chile," Resources Policy, Elsevier, vol. 76(C).
    8. Diao, Mi & Leonard, Delon & Sing, Tien Foo, 2017. "Spatial-difference-in-differences models for impact of new mass rapid transit line on private housing values," Regional Science and Urban Economics, Elsevier, vol. 67(C), pages 64-77.
    9. Wanqi Liu & Rong Zhao, 2026. "Does Entry of Food-and-Drink Establishments Raise Local House Prices? Event-Study Evidence from London," Papers 2603.03260, arXiv.org, revised Apr 2026.
    10. Wu, Xianhua & Tian, Zhiqing & Kuai, Yun & Song, Shunfeng & Marson, Stephen M., 2022. "Study on spatial correlation of air pollution and control effect of development plan for the city cluster in the Yangtze River Delta," Socio-Economic Planning Sciences, Elsevier, vol. 83(C).
    11. Yu, Yantuan & Zhang, Ning, 2021. "Low-carbon city pilot and carbon emission efficiency: Quasi-experimental evidence from China," Energy Economics, Elsevier, vol. 96(C).
    12. Chagas, André L.S. & Azzoni, Carlos R. & Almeida, Alexandre N., 2016. "A spatial difference-in-differences analysis of the impact of sugarcane production on respiratory diseases," Regional Science and Urban Economics, Elsevier, vol. 59(C), pages 24-36.
    13. Comber, Sam & Arribas-Bel, Dani, 2017. "“Waiting on the train”: The anticipatory (causal) effects of Crossrail in Ealing," Journal of Transport Geography, Elsevier, vol. 64(C), pages 13-22.
    14. Lu, Qing-Long & Qurashi, Moeid & Antoniou, Constantinos, 2023. "Simulation-based policy analysis: The case of urban speed limits," Transportation Research Part A: Policy and Practice, Elsevier, vol. 175(C).
    15. Maria Chiara Pietrogrande & Cristina Colombi & Eleonora Cuccia & Umberto Dal Santo & Luisa Romanato, 2023. "Seasonal and Spatial Variations of the Oxidative Properties of Ambient PM 2.5 in the Po Valley, Italy, before and during COVID-19 Lockdown Restrictions," IJERPH, MDPI, vol. 20(3), pages 1-16, January.
    16. Qiang Tu & Limei Zuo & Jianlei Mo & Yingnan Wang, 2026. "Carbon pricing, green innovation, and production efficiency—new evidence from China," Mitigation and Adaptation Strategies for Global Change, Springer, vol. 31(3), pages 1-32, March.
    17. Zhang, Yue-Jun & Liu, Zhao & Zhou, Si-Ming & Qin, Chang-Xiong & Zhang, Huan, 2018. "The impact of China's Central Rise Policy on carbon emissions at the stage of operation in road sector," Economic Modelling, Elsevier, vol. 71(C), pages 159-173.
    18. Du, Minzhe & Wu, Fenger & Luo, Lichun & Wang, Qiya & Liao, Liping, 2025. "Spatial effects of the market-based energy allocation on energy efficiency: A quasi-natural experiment of energy quota trading," Energy, Elsevier, vol. 318(C).
    19. Dohyo Jeong & Dohyeong Kim & Heba Mohiuddin & Seokmin Kang & Sungyeun Kim, 2023. "Regional Disparity in the Educational Impact of COVID-19: A Spatial Difference-in-Difference Approach," Sustainability, MDPI, vol. 15(16), pages 1-13, August.
    20. World Bank & Bedoya Arguelles,Guadalupe & Dolinger,Amy & Dolkart,Caitlin Fitzgerald & Legovini,Arianna & Sveta Milusheva & Marty,Robert Andrew & Taniform,Peter Ngwa, 2023. "The Unintended Consequences of Curfews on Road Safety," Policy Research Working Paper Series 10393, The World Bank.

    More about this item

    Keywords

    ;
    ;
    ;
    ;
    ;
    ;

    Statistics

    Access and download statistics

    Corrections

    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:eee:trapol:v:178:y:2026:i:c:s0967070x25005128. See general information about how to correct material in RePEc.

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    If CitEc recognized a bibliographic reference but did not link an item in RePEc to it, you can help with this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: Catherine Liu (email available below). General contact details of provider: http://www.elsevier.com/wps/find/journaldescription.cws_home/30473/description#description .

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service. RePEc uses bibliographic data supplied by the respective publishers.