Table 1: Studies focused on traffic-related air pollution (TRAP).

Source/yearOutdoor variablesAge groupSample sizeClimate regionStudy designAssessment methodFindings and limits

Asthma symptom
Bernstein, 2012TRAP (ECAT)1–7 years700Central, USCohort/adjustedMedical evaluations, skin testing, proximity, and LUR Higher TRAP associated with wheezing during infancy and at age 3. Limit: parental reports of wheezing at 3 are not strong asthma predictors

McConnell et al., 2010TRAP, PM10, PPM2.5, O3K-1st grade2,497Western, USCohort/adjustedBaseline and annual questionnaires, community ambient air pollution, weather variables, local TRAPAsthma risk increased with modeled TRAP from roadway near home (HR 1.51; 95% CI: 1.25–1.82) and near school (HR 1.45; 95% CI: 1.06–1.98). Limit: short 3-year follow-up

Sucharew et al., 2010TRAP, PM10, PM2.5,1–3 years550Central, USCohort/adjustedQuestionnaires, skin prick test, air quality monitoring, clinical evaluation, home visits, house dustChildren exposed to higher levels of TRAP are more likely to suffer recurrent night cough (OR, 1.45, 95% CI, 1.09–1.94) than children less exposed. Limit: sample is limited to those with high risk

Eckel et al., 2011TRAP, roads, traffic densities, NO, NO27–11 years2,143Western, USCross-sectional/adjustedBreath collection technique (offline and online), geocoding distance from residence to roads, road class, and density data, NO2 sampling/, questionnaire, body mass index,Length of roads positively was associated with FeNO, with significant associations in small buffers: 46.7% [95% CI, 14.3–88.4] higher FeNO for increases in the length of all roads in 50 m buffers. Limit: rely on parent report for medication use as a confounding factor

Asthma-related symptom and care utilization
Newman et al., 2014TRAP1–16 years758Central, USCohort/adjustedAdministrative data (ICD-9-CM) for hospital readmission (primary or secondary diagnosis), questionnaires, serum sample, allergen-specific IgE testingHigher TRAP exposure was associated with higher readmission rate (21% versus 16%; ), association was not significant after adjusting for covariates (aOR, 1.4; 95% CI, 0.9–2.2). Limit: sample was from one single institution

aOR: adjusted Odds Ratio; HR: Hazard Ratio; LUR: land use regression; ECAT: elemental carbon attributed to traffic. Note. (a) TRAP exposure estimated using a qualitative proximity model and quantitative LUR model; (b) modeled annual concentration estimates based on surrounding area characteristics (c) used several models including line source dispersion and regression models to map estimates.