Case Study:

Waterloo, Iowa

Methodology

Determine Impacts on Affected Population

The results of these steps can be combined in a number of ways, using GIS tools, to assess the social impacts of the transportation project:

• Maps of air pollution or noise contours can be overlaid graphically with maps showing total populations and populations of interest by census block (Figure 4).

Figure 4. Noise Contour Overlaid on Minority Population (detail)

• GIS analysis capabilities can be used to estimate the number of total, minority, or low-income persons who live within unacceptable noise or air pollution contours ("unacceptable" levels may be based on federal, state, or local guidelines). This can be done by first identifying the census blocks falling within a given emissions or noise contour, and then identifying the number of people in the population groups of interest living within these blocks. As a further refinement, for blocks that fall only partially within the contour, the proportion of the block falling within the contour can be calculated using a GIS overlay. This proportion can be multiplied by the total population of the block to determine the number of people adversely affected.

• Measures of affected population groups can be compared for conditions with and without a proposed transportation program, to evaluate the increase or decrease in affected persons as a result of the project. For example, to evaluate whether the program has a disproportionate impact on minority and low-income populations, the percent of total area-wide population adversely affected by the project could be compared by the percent of area-wide minority and low-income population that is adversely affected.

[TOP]