Commentary: Diesel, Cars, and Public Health

Rojas-Rueda, David; Turner, Michelle C.

doi: 10.1097/EDE.0000000000000427

From the aCentre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain; bMunicipal Institute of Medical Research (IMIM-Hospital del Mar), Barcelona, Spain; cUniversitat Pompeu Fabra (UPF), Departament de Ciències Experimentals i de la Salut, Barcelona, Spain; dCIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain; and eMcLaughlin Centre for Population Health Risk Assessment, University of Ottawa, Ottawa, ON, Canada.

Correspondence: David Rojas-Rueda, CREAL-Centre for Research in Environmental Epidemiology, Barcelona Biomedical Research Park, Dr. Aiguader, 88, 08003, Barcelona, Spain. E-mail:

Article Outline

In September 2015, the US Environmental Protection Agency (US EPA) issued a notice of violation of the Clean Air Act to the automobile manufacturer Volkswagen.1 It alleges that four-cylinder Volkswagen and Audi diesel vehicles from the years 2009–2015 included software that circumvented accurate emissions testing for certain air pollutants—in particular, nitrogen oxides (NOx). The US EPA and the California Air Resources Board determined that such vehicles emitted up to 40 times more NOx than current emission standards allow. It is estimated that there are a total of 11 million affected vehicles worldwide.

The Volkswagen violation of the Clean Air Act represents not only a violation of air quality law but also of public health due to the wide range of adverse health effects associated with exposure to NOx and nitrogen dioxide (NO2).2,3 A recent report on the impact of the Volkswagen violation estimated a total of 59 premature deaths in the US due to excess emissions by affected vehicles.4 Motor vehicles represent the largest source of human exposure to NO2.2

The mean population-weighted concentration of outdoor NO2 in the US was estimated to be 10.7 ppb based on a national land-use regression model for the year 2006.5 Worldwide, concentrations of NO2 are increasing most rapidly in parts of Eastern Asia, Europe, North Africa, and the Middle East and decreasing in North America and Oceania.6 Current NO2 standards are 53 ppb (annual mean) and 100 ppb (98th percentile of 1-hour daily maximum concentrations averaged over 3 years) in the US. The World Health Organization air quality guideline value for NO2 is 21 ppb (annual mean).2,7

Epidemiologic studies have reported consistent evidence that short-term exposure to NO2, of several hours to days, is associated with increases in all-cause mortality as well as a variety of respiratory and cardiovascular effects. A meta-analysis of 43 studies reported a 0.71% (95% confidence interval [CI] 0.43%, 1.00%) increase in risk for all-cause mortality per 10 µg/m3 increase in 24 hours NO2 concentrations.8 NO2 has also been associated with a variety of adverse respiratory health effects, including airway irritation, respiratory symptoms, and, in susceptible populations such as those with asthma, an increase in emergency room visits and hospital admissions.9,10 Recent meta-analyses have also indicated a role of short-term NO2 in risk of myocardial infarction,11 heart failure,12 and stroke.13

Long-term exposure to NO2, of several months to years, has also been related to increases in all-cause and cause-specific mortality. A recent meta-analysis of 19 studies reported a 4% (95% CI: 2%, 6%) increase in risk for total mortality per each 10 µg/m3 increase in NO2 concentrations and a 13% (95% CI: 9%, 18%) increase in risk for cardiovascular mortality which remained in multipollutant models adjusting for concentrations of particulate matter <2.5 μm in diameter (PM2.5).14 There were also small positive associations observed with both total and cardiovascular mortality in multipollutant models adjusting for both PM2.5 and ozone (O3) concentrations in recent studies in California and Canada.15,16

Long-term exposure to NO2 has also consistently been associated with a range of adverse respiratory effects including increases in asthma incidence and severity in children and decrements in lung function.17,18 There was an inverse association between NO2 and lung volume growth.19 NOx was also associated with exhaled nitric oxide (FeNO), an indicator of airway inflammation, in the California Children’s Health Study.20 In adults, a positive association between NO2 and incident adult wheeze was recently reported in the US Sister Study.21 Another study noted associations between NO2 and biomarkers of systemic inflammation in chronic obstructive pulmonary disease patients.22 There was a 3% (95% CI: 2%, 3%) increase in risk for respiratory mortality overall in a recent meta-analysis per each 10 µg/m3 NO2.14

The International Agency for Research on Cancer also has classified both ambient air pollution and diesel engine exhaust as group 1 human carcinogens.3,23 A meta-analysis of 20 epidemiologic studies reported a 4% (95% CI: 1%, 8%) increase in lung cancer risk per each 10 µg/m3 increase in NO2 concentrations.24 Evidence for other cancer sites is still unclear.

Currently, the US EPA is updating the policy-relevant science related to the health effects of NO2 in the review of the National Ambient Air Quality Standards (NAAQS).2 It is also important to note that NOx is an important contributor to the secondary formation of air pollutants including PM and O3, both of which have also been independently associated with a range of adverse human health effects.24–28

There are a number of interventions available to address the Volkswagen violation specifically including stopping the sale and production of affected vehicles, repairing vehicles sold during this time period, and improving verification of vehicle emissions throughout the automobile industry. Broader-scale interventions also include supporting the technological transition toward cleaner vehicles (natural gas, hydrogen, hybrid, and electric) to reduce in general emissions of NOx and other particulate and gaseous air pollutants.29,30 It is important to note, however, that there are still nonexhaust emissions from brakes, tires, clutch, and road surface wear that contribute nearly half of the total particle emissions from vehicles.31 The chemical composition of these includes various heavy metals, sulfur, organic compounds, elemental carbon, and PAHs, for example, which have also been associated with multiple adverse health effects.32,33

Although such technological interventions toward cleaner vehicles will result in large reductions in air pollution emissions, it is important to consider that alone they do not address the underlying public reliance on private vehicles for transport, which is an important determinant of public and population health, with impacts on traffic incidents, physical inactivity, and social and health inequalities. There is now accumulating evidence of large health cobenefits of urban transport policies that act to promote the replacement of car trips by public transport and active mobility (i.e., walking, cycling), including improvements in levels of physical activity, and reductions in levels of air pollution, noise, and traffic incidents.34 The Table provides a direct comparison of the potential impacts of technological transition versus a city model of public transport and active mobility. It is important to note that the city model does not exclude technological transition but rather represents a more holistic view of urban planning intervention.

Possible urban planning interventions to promote public transport and active mobility are presented in the Figure. Interventions include improvements to increase land-use mix, density, connectivity, intermodality, greenspaces, public transport and active mobility infrastructure, traffic calming, accessibility, aesthetics, traffic safety, reduction of crime, economic incentives for public transport and active mobility and disincentives for vehicle use and parking.35,36

Numerous studies have attempted to assess the impact of such urban planning interventions on rates of public transport use and active mobility. Improvements in cycling infrastructure, including increasing the number and quality of bike lanes, bike parking spaces, and traffic signals, resulted in two- to six-fold increases in cycling rates in a number of cities worldwide.37,38 Bike sharing systems have also been shown to further increase cycling rates in Europe.37,38 The implementation of rapid bus transit systems increased public transport use in several cities including Curitiba, Guangzhou, Jakarta, and Mexico City.39 Reductions in vehicle use were also observed in London, Singapore, and Stockholm following the implementation of a congestion charge, and in Berlin with the low emission zone.37

Clear public and population health benefits have been observed following the implementation of such urban planning interventions. Rates of walking and cycling were seen to increase directly through active mobility interventions, as well as indirectly through increases in the use of public transport, with clear health benefits for multiple health outcomes.34,40,41 Multiple health risk assessments have quantified estimated changes in physical activity levels through the substitution of car trips by public transport and active mobility, in terms of benefits for all-cause and cause-specific mortality, including cardiovascular disease, cancer, and other endpoints.34,42 A systematic review of 30 studies examining the impact of active transportation interventions estimated a median health benefit–risk or benefit–cost ratio of 9.34

Other cobenefits of car substitution include the reduction of air pollution and noise emissions.34 Although changes in physical activity levels only benefit travelers, reductions in air pollution and noise emissions benefit all city inhabitants.34,42 Car substitution is also associated with improvements in traffic safety, as public transport is one of the safest modes of urban transport.43 Improvements in active mobility infrastructure and increased driver awareness regarding pedestrians and cyclists also play a role.44

Furthermore, the implementation of an urban mobility model promoting public transport and active mobility can also contribute to reduce levels of social and health inequalities in the population.45,46 Disadvantaged groups may be disproportionally exposed to local environments which discourage physical activity and active mobility. They may also perceive their environment to have greater levels of traffic, fewer opportunities for walking, and have concerns regarding crime and levels of personal safety.47–49 Higher rates of traffic-related injuries and death have also been noted among lower socioeconomic groups.48 Enhanced public transport can improve mobility and access to services among the disadvantaged, as well as strengthen social relationships.45

In conclusion, the recent Volkswagen violation provides a valuable opportunity not only to support the technological transition required to reduce emissions from motor vehicles directly but also to reconsider our models of cities where both public transport and active mobility can contribute to healthier urban environments and populations. Such a transition requires a broader examination of urban planning and transport policies by relevant authorities, health practitioners, and citizens.

Back to Top | Article Outline


1. US EPA. Notice of violation of the clean air act. Available at: Accessed September 18, 2015
2. US EPA. US Environmental Protection Agency;. Integrated science assessment for oxides of nitrogen – health criteria (second external review draft, 2015). 2015 Washington, DC EPA/600/R-14/006
3. Benbrahim-Tallaa L, Baan RA, Grosse Y, et al.International Agency for Research on Cancer Monograph Working Group. Carcinogenicity of diesel-engine and gasoline-engine exhausts and some nitroarenes. Lancet Oncol. 2012;13:663–664
4. Barrett SRH, Speth RL, Eastham SD, et al. Impact of the Volkswagen emissions control defeat device on US public health. Environ Res Lett. 2015;10:114005
5. Novotny EV, Bechle MJ, Millet DB, Marshall JD. National satellite-based land-use regression: NO2 in the United States. Environ Sci Technol. 2011;45:4407–4414
6. Geddes JA, Martin RV, Boys BL, van Donkelaar A. Long-term trends worldwide in ambient NO2 concentrations inferred from satellite observations. Environ Health Perspect. 2015 Aug 4 [ePub ahead of print]
7. World Health Organization. WHO air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide. 2006 Geneva: Switzerland: World Health Organization
8. Mills IC, Atkinson RW, Kang S, Walton H, Anderson HR. Quantitative systematic review of the associations between short-term exposure to nitrogen dioxide and mortality and hospital admissions. BMJ Open. 2015;5:e006946
9. Alhanti BA, Chang HH, Winquist A, Mulholland JA, Darrow LA, Sarnat SE. Ambient air pollution and emergency department visits for asthma: a multi-city assessment of effect modification by age. J Expo Sci Environ Epidemiol. 2015 Sep 9 [ePub ahead of print]
10. Weichenthal S, Bélisle P, Lavigne E, et al. Estimating risk of emergency room visits for asthma from personal versus fixed site measurements of NO2. Environ Res. 2015;137:323–328
11. Mustafic H, Jabre P, Caussin C, et al. Main air pollutants and myocardial infarction: a systematic review and meta-analysis. JAMA. 2012;307:713–721
12. Shah AS, Langrish JP, Nair H, et al. Global association of air pollution and heart failure: a systematic review and meta-analysis. Lancet. 2013;382:1039–1048
13. Shah AS, Lee KK, McAllister DA, et al. Short term exposure to air pollution and stroke: systematic review and meta-analysis. BMJ. 2015;350:h1295
14. Faustini A, Rapp R, Forastiere F. Nitrogen dioxide and mortality: review and meta-analysis of long-term studies. Eur Respir J. 2014;44:744–753
15. Crouse DL, Peters PA, Hystad P, et al. Ambient PM2.5, O3, and NO2 exposures and associations with mortality over 16 years of follow-up in the Canadian census health and environment cohort (CanCHEC). Environ Health Perspect. 2015;123:1180–1186
16. Jerrett M, Burnett RT, Beckerman BS, et al. Spatial analysis of air pollution and mortality in California. Am J Respir Crit Care Med. 2013;188:593–599
17. Bowatte G, Lodge C, Lowe AJ, et al. The influence of childhood traffic-related air pollution exposure on asthma, allergy and sensitization: a systematic review and a meta-analysis of birth cohort studies. Allergy. 2015;70:245–256
18. Gehring U, Gruzieva O, Agius RM, et al. Air pollution exposure and lung function in children: the ESCAPE project. Environ Health Perspect. 2013;121:1357–1364
19. Mölter A, Agius RM, de Vocht F, et al. Long-term exposure to PM10 and NO2 in association with lung volume and airway resistance in the MAAS birth cohort. Environ Health Perspect. 2013;121:1232–1238
20. Berhane K, Zhang Y, Salam MT, et al. Longitudinal effects of air pollution on exhaled nitric oxide: the Children’s Health Study. Occup Environ Med. 2014;71:507–513
21. Young MT, Sandler DP, DeRoo LA, Vedal S, Kaufman JD, London SJ. Ambient air pollution exposure and incident adult asthma in a nationwide cohort of U.S. women. Am J Respir Crit Care Med. 2014;190:914–921
22. Dadvand P, Nieuwenhuijsen MJ, Agustí À, et al. Air pollution and biomarkers of systemic inflammation and tissue repair in COPD patients. Eur Respir J. 2014;44:603–613
23. Loomis D, Grosse Y, Lauby-Secretan B, et al.International Agency for Research on Cancer Monograph Working Group IARC. The carcinogenicity of outdoor air pollution. Lancet Oncol. 2013;14:1262–1263
24. Hamra GB, Guha N, Cohen A, et al. Outdoor particulate matter exposure and lung cancer: a systematic review and meta-analysis. Environ Health Perspect. 2014;122:906–911
25. Berman JD, Fann N, Hollingsworth JW, et al. Health benefits from large-scale ozone reduction in the United States. Environ Health Perspect. 2012;120:1404–1410
26. Forouzanfar MH, Alexander L, Anderson HR, et al. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks in 188 countries, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2015;386:2287–2323
27. Newby DE, Mannucci PM, Tell GS, et al.ESC Working Group on Thrombosis, European Association for Cardiovascular Prevention and Rehabilitation; ESC Heart Failure Association. Expert position paper on air pollution and cardiovascular disease. Eur Heart J. 2015;36:83–93b
28. World Health Organization. . Review of evidence on health aspects of air pollution-REVIHAPP project. 2013 Copenhagen, Denmark World Health Organization
29. Bauer C, Hofer J, Althaus HJ, Del Duce A, Simons A. The environmental performance of current and future passenger vehicles: life cycle assessment based on a novel scenario analysis framework. Applied Energy. 2015;157:871–883
30. Noshadravan A, Cheah L, Roth R, Freire F, Dias L, Gregory J. Stochastic comparative assessment of life-cycle greenhouse gas emissions from conventional and electric vehicles. Int J Life Cycle Assess. 2015;20:854–864
31. Grigoratos T, Martini G. Non-exhaust traffic related emissions. Brake and tyre wear PM. JRC Science and Policy Report, European Commission. 2014
32. Pant P, Harrison RM. Estimation of the contribution of road traffic emissions to particulate matter concentrations from field measurements: A review. Atmos Environ. 2013;77:78–97
33. Kelly FJ, Fussell JC. Size, source and chemical composition as determinants of toxicity attributable to ambient particulate matter. Atmos Environ. 2012;60:504e–526e
34. Mueller N, Rojas-Rueda D, Cole-Hunter T, et al. Health impact assessment of active transportation: a systematic review. Prev Med. 2015;76:103–114
35. Ewing R, Cervero R. Travel and the built environment: a meta-analysis. J Am Plann Assoc. 2010;76:265–294
36. World Health Organization. Reducing global health risks through mitigation of short-lived climate pollutants. 2015 Geneva, Switzerland World Health Organization
37. United Nations. Shanghai manual a guide for sustainable urban development in the 21st century. 2010 New York: United Nations
38. Pucher J, Dill J, Handy S. Infrastructure, programs, and policies to increase bicycling: an international review. Prev Med. 2010;50(Suppl 1):S106–S125
39. Cervero R. Bus rapid transit (BRT): an efficient and competitive mode of public transport. Institute for Urban and Regional Development. 2013
40. Kelly P, Kahlmeier S, Götschi T, et al. Systematic review and meta-analysis of reduction in all-cause mortality from walking and cycling and shape of dose response relationship. Int J Behav Nutr Phys Act. 2014;24:111–132
41. Rissel C, Curac N, Greenaway M, Bauman A. Physical activity associated with public transport use–a review and modelling of potential benefits. Int J Environ Res Public Health. 2012;9:2454–2478
42. Rojas-Rueda D, de Nazelle A, Teixidó O, Nieuwenhuijsen MJ. Health impact assessment of increasing public transport and cycling use in Barcelona: a morbidity and burden of disease approach. Prev Med. 2013;57:573–579
43. Savage I. Comparing the fatality risks in the United States transportation across modes and over time. Res Transp Econ. 2013;43:9–22
44. Jacobsen PL. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Inj Prev. 2003;9:205–209
45. European Parliament. . Social inclusion in EU public transport. Directorate-General for Internal Policies. European Union. 2015
46. Turrell G, Haynes M, Wilson LA, Giles-Corti B. Can the built environment reduce health inequalities? A study of neighbourhood socioeconomic disadvantage and walking for transport. Health Place. 2013;19:89–98
47. Giles-Corti B, Donovan RJ. Socioeconomic status differences in recreational physical activity levels and real and perceived access to a supportive physical environment. Prev Med. 2002;35:601–611
48. Gorman D, Douglas MJ, Conway L, Noble P, Hanlon P. Transport policy and health inequalities: a health impact assessment of Edinburgh’s transport policy. Public Health. 2003;117:15–24
49. Saelens BE, Sallis JF, Black JB, Chen D. Neighborhood-based differences in physical activity: an environment scale evaluation. Am J Public Health. 2003;93:1552–1558
Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.