Speed limits and their effect on air pollution in Mexico City: A quasi-experimental study

Speed limits are an evidence-based intervention to prevent traffic collisions and deaths, yet their impact on air pollution in cities is understudied. The objective of this study was to investigate the association between lower speed limits and air pollution. We leverage the introduction of a new ro...

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Bibliographic Details
Published in:The Science of the total environment 2024-05, Vol.924, p.171506-171506, Article 171506
Main Authors: Texcalac-Sangrador, Jose Luis, Pérez-Ferrer, Carolina, Quintero, Carolina, Prado Galbarro, Francisco-Javier, Yamada, Goro, Gouveia, Nelson, Barrientos-Gutierrez, Tonatiuh
Format: Article
Language:English
Subjects:
Air pollution
City
Mexico
Policy
Road safety
Speed
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Summary:Speed limits are an evidence-based intervention to prevent traffic collisions and deaths, yet their impact on air pollution in cities is understudied. The objective of this study was to investigate the association between lower speed limits and air pollution. We leverage the introduction of a new road safety policy in Mexico City in December 2015 which lowered speed limits, increased fines, and installed speed radars to enforce compliance. We tested whether the policy had an impact on particulate matter (PM2.5) and nitrogen dioxide (NO2) at the city level, and whether air-quality monitoring stations' proximity to speed radars moderated this effect due to more acceleration and deceleration around radars. NO2 and PM2.5 concentrations from January 2014 to December 2018 were obtained from the National System of Air Quality Information. Air-quality monitoring stations were classified as in close-proximity or far-from-speed radars. Interrupted time series analyses were conducted for each outcome separately, using linear mixed models and adjusting for seasonality and time-varying confounders: registered vehicles, temperature, wind-speed and relative humidity. The results suggest improvement in both contaminants after the speed limits policy. For NO2, the pre-policy trend was flat, while the post-policy trend showed a decline in concentrations of 0.04 ppb/week. For PM2.5, concentrations were increasing pre-policy by 0.08 μg/m3 per week, then this trend flattened in the post-policy period to a weekly, non-significant, increase of 0.03 μg/m3 (p = 0.08). Air-quality monitors' proximity to speed radars did not moderate the effect of the policy on either of the pollutants. In conclusion, the speed limits policy implemented in Mexico City in 2015 was associated with improvements in air pollution. [Display omitted] •Speed limits are recommended for road safety but may impact air pollution.•We evaluated a new speed limits policy implemented in Mexico City.•NO2 and PM2.5 concentrations improved after speed limits policy was implemented.•Air quality monitors' proximity to speed radars did not modify NO2 or PM2.5 readings.
ISSN:0048-9697
1879-1026
DOI:10.1016/j.scitotenv.2024.171506