Editor's Note: A recent Planetizen blog post by the University of South Florida's Steven Polzin voiced several criticisms about the Housing + Transportation (H+T®) Affordability Index, created by the Chicago-based Center for Neighborhood Technology (CNT). We have provided a venue for Scott Bernstein, founder and president of CNT, to respond below.
CNT's H+T Index Fills Gaps in Data that Others Don't Provide
The purpose of the Center for Neighborhood Technology's Housing + Transportation (H+T®) Affordability Index is to reveal the hidden cost of transportation as a function of the built environment at a meaningful geography (the neighborhood). CNT developed the H+T Index to provide a single source of information on housing and transportation costs at the neighborhood level for metropolitan areas across the United States. The Index provides a more comprehensive way to estimate and display the difference between the cost of housing and true affordability. There are many data sources that provide neighborhood-level housing-cost data. But there is no other national data source for household transportation costs at this scale. The tool, which covers 179,000 Census block groups, is designed to help individuals, planners, and policymakers to more fully grasp and act on the relationship between development patterns, transportation behavior, and household transportation costs. Aggregating data to geographies such as rural, urban, suburban, and regional provides results that are too coarse to inform people and policymakers' important real-world, place-based decisions.
The methods used to create the H+T Index are supportable and independently verified. The method used to create the H+T Index was first vetted and published by the Brookings Institution in 2006 and then in the Transportation Research Record of the Transportation Research Board in 2008. It was thoroughly vetted by a team from the University of Pennsylvania in 2012 for the US Dept. of Housing and Urban Development, which found that "The strengths of the H+T Index center on the simplicity with which the results can be presented and understood and on their comparability. In addition, the index has benefitted from a rigorous approach to both data assembly and statistical modeling " That same review offered practical suggestions for future improvements, which CNT is initiating.
The transportation costs in the Index are estimates for a hypothetical, typical family in order to isolate the effect that the built environment has on those costs. The H+T Index was constructed to estimate three dependent variables (auto ownership, auto use, and transit use) as functions of 11 independent variables (median income, per capita income, average household size, average commuters per household, residential density, gross density, average block size, intersection density, transit connectivity, transit access shed, and employment access). To get at the built environment's influence on transportation costs, the independent household variables (income, household size, and commuters per household) are set at fixed values to control for any variation they might cause. By establishing and running the model for a "typical household" (one defined as earning the regional area median income, having the regional average household size, and having the regional average number of commuters per household), any variation observed in transportation costs is due to place and location, not household characteristics.
CNT knows that auto costs in the Index aren't perfect. We have revisited the auto-cost measure each time that we have improved the Index. We acknowledge there is a distinction between the long-term costs of new and used vehicles, but that data is not publicly available from either an industry leader or government source. Even if we were able to separate auto costs based on whether households drove a new or used car, we suspect that the increased costs associated with a used vehicle-significantly more repairs and maintenance and likely higher fuel costs due to efficiency decay-will at least partially offset the used-car cost savings described in Polzin's recent post. And in keeping with the idea that the H+T Index is an index, variables such as these should be held constant so as to provide a valid geographic comparison.
CNT created the H+T Index as a public service to fill gaps in data that the federal government does not provide. Policymakers, planners, investors, community leaders, and households all need good information to make good investment and location decisions. The H+T Index provides an important resource-community-scale transportation costs-that standard federal and industry sources don't offer.
We all live in a world where the economy has not yet fully recovered, the population composition is changing, policymakers are seeking strategies to minimize exposure to future shocks, and unproductive public investing is no longer an option. We welcome additional ideas and further research on solutions to these challenges that people and policymakers can make use of in the here and now.