Travel Impacts on Air Quality and Greenhouse Gases
Data demonstrates that emissions of air pollutants and greenhouse gases increase with vehicle miles driven. Therefore, the more automobile and truck traffic, the greater amount of pollutants emitted.
Research also shows an association between asthma and air quality, as well as life expectancy. Reducing traffic by increasing walkability and bikeability can improve the quality of air that we breathe and cut down on emission of air pollutants and greenhouse gases.
The literature in this section relates to vehicle emissions, air pollution, travel behaviors, and health opportunities.
- It is estimated that reductions in air pollution account for as much as 15% of the overall increase in life expectancy in study areas (Pope, et al., 2009).
- In a scenario without buses, city-wide schools (as compared with neighborhood schools) have six times fewer children walking to school, 4.5 times more miles traveled, 4.5 times the system cost and 4.5 times the emissions of criteria air pollutants and greenhouse gases (Wilson, et al., 2007).
- Bus service can decrease miles traveled and resulting emissions by 60-70% compared to no bus service (Wilson, et al., 2007).
- A 5% increase in neighborhood walkability is associated with:
- 6.5% fewer vehicle miles traveled (VMT) per capita
- 5.6% fewer grams of Nitrogen Dioxide per capita
- 5.5% fewer grams of volatile organic compound (VOC) emitted per capita (Frank, et al., 2006)
- Results demonstrate an association between increased asthma and closer residential distance to a freeway, indicating that respiratory health in children is adversely affected by local exposures to outdoor Nitrogen Dioxide or other freeway-related pollutants (Gauderman, et al., 05).
- Substitution of cycling for driving for short trips has the potential to reduce gasoline demand up to nearly 34.9% of current domestic oil consumption (Higgins, et al., 2005).
- CONTEXT: Exposure to elevated concentrations of traffic-related air pollutants in the near-road environment is associated with numerous adverse human health effects, including childhood cancer, which has been increasing since 1975. Results of individual epidemiologic studies have been inconsistent. Therefore, a meta-analysis was performed to examine the association between residential traffic exposure and childhood cancer.
- EVIDENCE ACQUISITION: Studies published between January 1980 and July 2011 were retrieved from a systematic search of 18 bibliographic databases. Nine studies meeting the inclusion criteria were identified. Weighted summary ORs were calculated using a random effects model for outcomes with four or more studies. Subgroup and sensitivity analyses were performed.
- EVIDENCE SYNTHESIS: Childhood leukemia was positively associated (summary OR=1.53, 95% CI=1.12, 2.10) with residential traffic exposure among seven studies using a postnatal exposure window (e.g., childhood period or diagnosis address) and there was no association (summary OR=0.92, 95% CI=0.78, 1.09) among four studies using a prenatal exposure window (e.g., pregnancy period or birth address). There were too few studies to analyze other childhood cancer outcomes.
- CONCLUSIONS: Current evidence suggests that childhood leukemia is associated with residential traffic exposure during the postnatal period, but not during the prenatal period. Additional well-designed epidemiologic studies that use complete residential history to estimate traffic exposure, examine leukemia subtypes, and control for potential confounding factors are needed to confirm these findings. As many people reside near busy roads, especially in urban areas, precautionary public health messages and interventions designed to reduce population exposure to traffic might be warranted.
Boothe VL, Boehmer TK, Wendel AM, Yip FY. (2014). Residential Traffic Exposure and Childhood Leukemia: A Systematic Review and Meta-analysis. Am J Prev Med, 46(4), 413-422. doi: 10.1016/j.amepre.2013.11.004.
- Recent epidemiological research suggests that near road traffic-related pollution may cause chronic disease. Childhood asthma attributable to air pollution in 10 European cities was estimated by calculating the number of cases of 1) asthma caused by near road traffic-related pollution, and 2) acute asthma events related to urban air pollution levels. The researchers then expanded their approach to include coronary heart diseases in adults.
- Derivation of attributable cases required combining concentration-response function (CRF) between exposures and the respective health outcome of interest (obtained from published literature), an estimate of the distribution of selected exposures in the target population, and information about the frequency of the assessed morbidities.
- Exposure to roads with high vehicle traffic, a proxy for near road traffic-related pollution, accounted for 14% of all asthma cases. When a causal relationship between near road traffic- related pollution and asthma is assumed, 15% of all episodes of asthma symptoms were attributable to air pollution. Without this assumption, only 2% of asthma symptoms were attributable to air pollution. Similar patterns were found for coronary heart diseases in older adults. In the discussion, the authors suggest that their estimate of cases is likely low, due to under-reporting of cases. They point out that proximity to traffic will vary across an urban area, so finer analyses may be needed to tease out relationships between air quality and chronic disease burden.
- The authors conclude that pollutants along busy roads are responsible for a large and preventable share of chronic disease and related acute exacerbation in European urban areas.
Perez L, Declercq C, Aguilera I, et al. (2013). Chronic burden of near-roadway traffic pollution in 10 European cities (APHEKOM network). Eur Respir J. 2013 Mar 21.
- Background: Greenhouse gas emissions (GHGE) linked to climate change is the biggest threat to public health worldwide. California generates 7% of the US GHGE, and is the 12th largest emitter worldwide. Within transportation, the largest emitting sector in California (38%) and personal vehicles are the largest portion of that sector (79%). Two strategies to reduce emissions include increased use of clean emission vehicles and reducing miles driven. The latter approach would have the public health benefit of improved health from active transportation and reduced air pollution. The authors quantified transportation strategies to reduce greenhouse gas emissions using both approaches.
- Statistics on travel patterns and injuries, physical activity, fine particulate matter, and GHGE in the San Francisco Bay Area, California, were input into a model that calculated the health impacts of walking and bicycling short distances usually traveled by car or driving low-emission automobiles. The change in disease burden was calculated in disability-adjusted life years (DALYs) based on dose–response relationships and the distributions of physical activity, particulate matter, and traffic injuries.
- Increasing median daily walking and bicycling from 4 to 22 minutes reduced the burden of cardiovascular disease and diabetes by 14% (32466 DALYs), increased the traffic injury burden by 39% (5907 DALYS), and decreased GHGE by 14%. Low-carbon driving reduced GHGE by 33.5% and cardiorespiratory disease burden by less than 1%.
- Increased physical activity associated with active transport could generate a large net improvement in population health. Measures would be needed to minimize pedestrian and bicyclist injuries. Together, active transport and low-carbon driving could achieve GHGE reductions sufficient for California to meet legislative mandates of reducing emissions to 80% of 1990 levels levels by 2050.
Neil Maizlish, PhD, James Woodcock, PhD, Sean Co, MS, Bart Ostro, PhD, Amir Fanai, CEng IMechE, and David Fairley, PhD. (2013). Health Cobenefits and Transportation-Related Reductions in Greenhouse Gas Emissions in the San Francisco Bay Area. Am J Public Health, e1-e7. doi: doi:10.2105/AJPH. 2012.300939
- Recent research suggests the burden of childhood asthma that is attributable to air pollution has been underestimated in traditional risk assessments, and there are no estimates of these associated costs.
- This study aimed to estimate the yearly childhood asthma-related costs attributable to air pollution for Riverside and Long Beach, CA, USA, including: 1) the indirect and direct costs of healthcare utilization due to asthma exacerbations linked with traffic-related pollution (TRP); and 2) the costs of health care for asthma cases attributable to local TRP exposure.
- The authors calculated costs using estimates from peer-reviewed literature and the authors’ analysis of surveys (Medical Expenditure Panel Survey, California Health Interview Survey, National Household Travel Survey, and Health Care Utilization Project).
- A lower-bound estimate of the asthma burden attributable to air pollution was US$18 million yearly. Asthma cases attributable to TRP exposure accounted for almost half of this cost. The cost of bronchitic episodes was a major proportion of both the annual cost of asthma cases attributable to TRP and of pollution-linked exacerbations.
- Traditional risk assessment methods underestimate both the burden of disease and cost of asthma associated with air pollution, and these costs are borne disproportionately by communities with higher than average TRP.
Brandt, S. J., L. Perez, et al. (2012). Costs of Childhood Asthma Due to Traffic-Related Pollution in Two California Communities. European Respiratory Journal 40(2): 363-370.
- The emerging consensus that exposure to near-roadway traffic-related pollution causes asthma has implications for compact urban development policies designed to reduce driving and greenhouse gases.
- The authors estimated the current burden of childhood asthma-related disease attributable to near-roadway and regional air pollution in Los Angeles County (LAC) and the potential health impact of regional pollution reduction associated with changes in population along major traffic corridors. The burden of asthma attributable to the dual effects of near-roadway and regional air pollution was estimated, using nitrogen dioxide and ozone as markers of urban combustion-related and secondary oxidant pollution, respectively.
- The authors also estimated the impact of alternative scenarios that assumed a 20% reduction in regional pollution in combination with a ± 3.6% increase in the proportion of the total population living near major roads, a proxy for near-roadway exposure.
- The authors estimated that 27,100 cases of childhood asthma (8% of total) in LAC were at least partly attributable to pollution associated with residential location within 75m of a major road. As a result, a substantial proportion of asthma-related morbidity is a consequence of near-roadway pollution, even if symptoms are triggered by other factors. Benefits resulting from a 20% regional pollution reduction varied markedly depending on the associated change in near-roadway proximity.
- Study findings suggest that there are large and previously unappreciated public health consequences of air pollution in LAC and probably in other metropolitan areas with dense traffic corridors. To maximize health benefits, compact urban development strategies should be coupled with policies to reduce near-roadway pollution exposure.
Perez, L., F. Lurmann, et al. (2012) Near-Roadway Pollution and Childhood Asthma: Implications for Developing “Win-Win” Compact Urban Development and Clean Vehicle Strategies. Environmental Health Perspectives 120:1619–1626
- Autism is a heterogeneous disorder with genetic and environmental factors likely contributing to its origins. Examination of hazardous pollutants has suggested the importance of air toxics in the etiology of autism, yet little research has examined its association with local levels of air pollution using residence-specific exposure assignments. This study examines the relationship between traffic-related air pollution, air quality, and autism.
- This population-based case-control study includes data obtained from 279 children with autism and 245 control children with typical development who were enrolled in the Childhood Autism Risks from Genetics and the Environment study in California.
- The mother's address from the birth certificate and addresses reported from a residential history questionnaire were used to estimate exposure for each trimester of pregnancy and first year of life. Traffic-related air pollution was assigned to each location using a line-source air-quality dispersion model. Regional air pollutant measures were based on the Environmental Protection Agency's Air Quality System data. Logistic regression models compared estimated and measured pollutant levels for children with autism and for control children with typical development. The main outcome measures were crude and multivariable adjusted odds ratios (AORs) for autism.
- Children with autism were more likely to live at residences that had the highest quartile of exposure to traffic-related air pollution, during gestation and during the first year of life, compared with control children. All regional pollutant estimates were scaled to twice the standard deviation of the distribution for all pregnancy estimates.
- Exposure to traffic-related air pollution, nitrogen dioxide, PM2.5, and PM10 during pregnancy and during the first year of life was associated with autism. Further epidemiological and toxicological examinations of likely biological pathways will help determine whether these associations are causal.
Volk H.E., Lurmann, F., Penfold, B., Hertz-Picciotto, I., McConnell, R. (2012). Traffic-Related Air Pollution, Particulate Matter, and Autism. Archives of General Psychiatry 1-7.
- Automobile exhaust contains precursors to ozone and fine particulate matter (PM ≤ 2.5 µm in aerodynamic diameter; PM2.5), posing health risks. Dependency on car commuting also reduces physical fitness opportunities.
- In this study, the authors sought to quantify benefits from reducing automobile usage for short urban and suburban trips.
- The authors simulated census-tract level changes in hourly pollutant concentrations from the elimination of automobile round trips ≤ 8 km in 11 metropolitan areas in the upper Midwestern United States using the Community Multiscale Air Quality (CMAQ) model. Next, they estimated annual changes in health outcomes and monetary costs expected from pollution changes using the U.S. Environmental Protection Agency Benefits Mapping Analysis Program (BenMAP). In addition, the authors used the World Health Organization Health Economic Assessment Tool (HEAT) to calculate benefits of increased physical activity if 50% of short trips were made by bicycle.
- The authors estimate that, by eliminating these short automobile trips, annual average urban PM2.5 would decline by 0.1 µg/m3 and that summer ozone (O3) would increase slightly in cities but decline regionally, resulting in net health benefits of $4.94 billion/year [95% confidence interval (CI): $0.2 billion, $13.5 billion), with 25% of PM2.5 and most O3 benefits to populations outside metropolitan areas. Across the study region of approximately 31.3 million people and 37,000 total square miles, mortality would decline by approximately 1,295 deaths/year (95% CI: 912, 1,636) because of improved air quality and increased exercise. Making 50% of short trips by bicycle would yield savings of approximately $3.8 billion/year from avoided mortality and reduced health care costs (95% CI: $2.7 billion, $5.0 billion]. They also estimate that the combined benefits of improved air quality and physical fitness would exceed $8 billion/year.
- The study findings suggest that significant health and economic benefits are possible if bicycling replaces short car trips. Less dependence on automobiles in urban areas would also improve health in downwind rural settings.
Grabow, M. L., S. N. Spak, et al. (2012). “Air Quality and Exercise-Related Health Benefits from Reduced Car Travel in the Midwestern United States.” Environmental Health Perspectives 120(1): 68.
- This study assessed the forecasted health impacts associated with different strategies to reduce GHG from automobiles.
- Governmental researchers from CDPH and Bay Area transportation and air quality organizations teamed up with researchers from the London School of Hygiene and Tropical Medicine to try to answer the question: "What might be the health benefits or harms associated with active transport or low carbon driving?"
- The current research attempted to adapt this model to the health and travel patterns of Bay Area residents. The model uses statistical data on deaths, life shortening illness and injury, and years living with disability for major health conditions strongly linked to physical activity, traffic injuries, and the fine particles in air pollution that can reach deep into the lungs.
- At high levels of active transport, the model predicts annually 13% fewer premature deaths and 15% fewer years of life lost for cardiovascular disease and diabetes and 5% reductions in each of four other chronic diseases. After accounting for a 19% increase in the disease burden from fatal and serious traffic injuries to pedestrians and bicyclists, the Bay Area would still experience annually 2,236 fewer deaths and 22,807 years of life gained.
- Because it reduces air pollution, low carbon driving yields 22 fewer deaths and a gain of 232 years of life lost from heart and respiratory disease; however, increased physical activity rather than less air pollution accounts for almost all the health benefits. While low carbon driving generated little health co-benefits, it is estimated to reduce GHG emissions 9% to 33.5% from the 2000 baseline. The most ambitious active transport scenario would achieve from 9% to 14.5% in GHG reductions.
- Reducing risks from chronic disease of the magnitude suggested by this research would reduce the estimated $34 billion annual cost in California from cardiovascular disease and other chronic conditions such as obesity.
Maizlish, N., J. Woodcock, et al. "Health Co-Benefits and Transportation-Related Reductions in Greenhouse Gas Emissions in the Bay Area: Technical Report."
- The role of exposure to air pollution in the development of allergic sensitization remains unclear.
- We sought to assess the development of sensitization until school age related to longitudinal exposure to air pollution from road traffic.
- More than 2500 children in the birth cohort BAMSE (Children, Allergy, Milieu, Stockholm, Epidemiological Survey) from Stockholm, Sweden, were followed with repeated questionnaires and blood sampling until 8 years of age. Outdoor concentrations of nitrogen oxides, as a marker of exhaust particles, and particles with an aerodynamic diameter of less than 10 μm (PM10), mainly representing road dust, were assigned to residential, day care, and school addresses by using dispersion models. Time-weighted average exposures were linked to levels of IgE against common inhalant and food allergens at 4 and 8 years of age.
- Air pollution exposure during the first year of life was associated with an increased risk of pollen sensitization at 4 years of age (odds ratio, 1.83; 95% confidence interval, 1.02-3.28) for a 5th to 95th difference in exposure to nitrogen oxides. At 8 years, there was no general increase in the risk of sensitization; however, the risk of food sensitization was increased, particularly among children free of sensitization at 4 years of age (odds ratio, 2.30; 95% confidence interval, 1.10-4.82). Results were similar by using PM10. No associations between air pollution exposure after the first year of life and sensitization were seen.
- Traffic-related air pollution exposure does not seem to increase the overall risk of sensitization to common inhalant and food allergens up to school age, but sensitization to certain allergens might be related to exposure during infancy.
Gruzieva, O., T. Bellander, et al. (2012). "Traffic-related air pollution and development of allergic sensitization in children during the first 8 years of life." Journal of Allergy and Clinical Immunology 129(1): 240-246.