Adjusting Computer Modeling Tools to Capture Effects of Smart Growth: Or “Poking at the Project Like a Lab Rat”

A developer in Atlanta, Georgia, asked the U.S. Environmental Protection Agency (EPA) to allow construction of a bridge that would make viable a proposed mixed-use development on an industrial site near downtown Atlanta. The construction would not be allowed, given Atlanta’s Clean Air Act conformity lapse, unless EPA found that the bridge, and the development it enabled, would reduce air emissions. EPA’s evaluation of the request was the agency’s first explicit examination, in a regulatory context, of urban planning as a means of reducing air pollution. As part of evaluating the developer’s petition, an EPA consultant team developed and applied innovative travel forecasting methods to accurately reflect the differences in transportation impacts among different development designs for the Atlantic Steel site. The methods also compare the impacts associated with developing the Atlantic Steel in-fill site with those of pushing the development into more remote “greenfield” areas of the region. The team devised a series of enhancements to the conventional travel forecasting methods, related to zone structure and trip-length profiles, network connectivity for intrazonal and neighboring-zone travel, representation of transit accessibility, influence of parking costs, recognition of nonmotorized travel, sensitivity to pedestrian environment factors, and sensitivity to site design based on the latest national research. With the help of these forecasting and analysis methods, the Atlantic Steel site studies show that certain site design amenities reduce travel. They also show that, when both regional location and site design enable people to travel by a mix of modes, measurably lower emissions and environmental impacts result.