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Case Study:
Waterloo, Iowa
Methodology
Estimate Emissions Impacts
The next step is to estimate the emissions and the spatial extent of these emissions from existing or planned roadway facilities. This involves three primary substeps:
- Use an emission factor model such as the EPA's MOBILE5 or PART5 to estimate emission rates based on traffic speed and composition. If emission factors for the local traffic fleet have already been developed by the regional metropolitan planning organization or air quality agency, it may be possible to utilize these factors.
- Use a dispersion model such as CAL3QHC® to estimate pollutant concentrations based on traffic speeds and volumes, intersection characteristics, lane widths, and wind speed and direction.
- Use GIS software to create maps showing pollutant concentration contours, overlaid on maps showing the street network and census blocks to be affected by the project.
CAL3QHC provides outputs in the form of pollutant concentrations at various user-specified X-Y coordinates. These concentrations can be plotted in GIS using a grid-based modeling package such as is included in ArcView Spatial Analyst or MapInfo Professional. The GIS software contains built-in interpolation algorithms that can be used to plot contours of emission concentration, based on the X-Y concentration data. (The X-Y coordinates used to identify link locations and receptor endpoints in CAL3QHC should be consistent with the coordinates used to map the road network in the GIS software.)
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