Near-residence traffic density.
Major roadway proximity and near-residence traffic density.
Prenatal and childhood near-residence traffic density, BC, and PM2.5 did not display consistent patterns of association with child cognition.
We estimated residential proximity to nearest major roadway and near-residence traffic density at birth and date of the mid-childhood cognitive assessment.
Children with higher near-residence traffic density at birth had slightly higher nonverbal IQ, visual motor, design memory, and picture memory scores (Table 3).
For periods in late pregnancy and childhood, we estimated spatially and temporally resolved black carbon (BC) and fine particulate matter (PM2.5) exposures, residential proximity to major roadways, and near-residence traffic density.
Exposure was assessed in several ways: residential proximity to major roadways, near-residence traffic density, and BC and fine particulate matter (aerodynamic diameter ≤ 2.5 μm; PM2.5) estimated at the residence level.
In addition, we assessed effect measure modification of associations with near-residence traffic density, BC, and PM2.5 by child sex and annual household income at assessment (< or ≥ $70,000) using interaction terms.
Near-residence traffic density was estimated as the length of all roads (kilometers) within 100 m of the residence multiplied by traffic counts on those roads (vehicles/day) [as in Zeka et al. (2008)], using traffic count data published by the Massachusetts Department of Transportation through the Office of Geographic Information (MassGIS 2014).
We used two main markers of exposure to ambient air pollution to assign long-term residential exposure to each subject, namely the modeled average home outdoor level of PM2.5 and the distance of the residence from traffic corridors, a widely used marker of exposure to unmeasured traffic-related pollutant concentrations [18].
