Analyzing Traffic-Related Air Pollution Exposure in the Philadelphia Area
It has been suggested through previous studies that exposure to traffic-related air pollution (TRAP) can increase the risk for the development and persistence of asthma. Particularly, communities of color and those in poverty appear more strongly affected by TRAP exposure near their homes. To further explore the potential relationship between air pollution and asthma rates of at-risk groups, my project aimed to determine whether traffic volume was higher in regions of the Greater Philadelphia area with higher proportions of minority groups and/or residents in poverty.
For the data analysis, we used demographic variables and census tracts defined by the US Census and American Community Survey (ACS) and downloaded traffic data from the Pennsylvania Department of Transportation. From these sources, we estimated the annual average daily traffic (AADT) for local roadways, converted AADT to daily vehicle miles traveled (DVMT), and coded shapefiles for Philadelphia, Bucks, Chester, Delaware, and Montgomery counties. We then overlaid DVMT rasters on county shapefiles to map tract-level DVMT and DVMT/m^2. Finally, to find the relationship between demographic variables against tract-level traffic volume, we calculated the regression of DVMT/m^2 versus ACS characteristics by plotting scatter plots with linear models.
By comparing the coefficients of these regression models, we could see that the demography of census tracts with the highest traffic volume in Philadelphia County appears to differ from the demography observed in the Five-County Area (FCA) and deviates from our hypothesized patterns. For example, an increased percentage of the White population is associated with a positive change in DVMT/m^2 in Philadelphia while associated with a negative change in the rest of the FCA. The opposite is true for an increased percentage of the Black population and population below the poverty line. It is possible that this deviation from expectations may be explained by Philadelphia’s large Black population and placement of highways near major tourist areas as opposed to residential neighborhoods like in the other counties. Further steps for this project are planned to find the exact difference in the relationship between tract-level ACS variables and traffic volume in Philadelphia and the FCA.