Housing and Transportation Affordability Index

H+T Index data is presented on a color-coded map. Source: Housing and Transportation Affordability Index

Introduction

Traditional housing affordability numbers look just at the cost of the housing itself. Transportation costs are not included, yet these costs are heavily reliant on housing. The Housing and Transportation (H+T®) Affordability Index combines both housing and transportation costs in an effort to present a more complete view of neighborhood affordability. Typically housing affordability is measured as 30% of household income; the H+T Index adds in 15% of income for transportation to set a combined affordability threshold of 45% of household income.

The H+T Index was originally created by the Center for Neighborhood Technology (CNT) as a project of the Brookings Institution's Urban Markets Initiative.

How it Works

The H+T Index overlays combined housing and transportation affordability data onto a map, making it easy to assess the location efficiency of a particular area. The map can be subdivided to the census block group level or bigger geographical units like tract, municipality, county, and Congressional District. Costs are presented as a percentage of household income, which can be set to regional typical, regional moderate, or national typical level. The map is color coded to highlight overall trends in affordability. The map also gives access to measures like autos per household, transit ridership as a percentage of workers, and annual transit cost. Data from the Index can be downloaded for free to let users perform their own analyses.

Besides the main Index map, the website contains three other tools to help use its data:

H+T Fact Sheets

The Index can automatically generate printable reports on individual municipalities, counties, CBSAs, MPOs and Congressional Districts. These reports provide a summary of the location efficiency and transportation costs of an area, as well as a detailed list of all the variables used by the Index.

Total Driving Costs

While gas is the most obvious cost of driving, the costs of owning and maintaining a car are generally much higher. This tool lets users input the price of gas and see the monthly or annual cost of both gas and car ownership in a particular area.

Comparison Maps

The Index can present several types of comparison maps.

Two Views of Affordability - With this interface, it is possible to select a specific area and simultaneously view the cost of housing and the combined cost of housing and transportation.
Greenhouse Gas Emissions - This interface shows greenhouse gas emissions per household compared to emissions per acre, highlighting the emissions efficiency of dense neighborhoods.
Custom Comparisons - Users can also create their own comparisons. This makes it possible to compare two different variables at the same or different locations.

The H+T Index was created by performing a regression analysis of the relationship between neighborhood characteristics and transportation habits. Source: Housing and Transportation Affordability Index

Methodology

The heart of the H+T Index is a transportation costs model designed by CNT.^[1] Three dependent variables - auto ownership, auto use, and transit use - are used to calculate the transportation costs of a location. The model uses regression analysis to estimate the relationship between these three dependent variables and a variety of neighborhood characteristics like income, density, and transit connectivity. The analysis draws data from nine sources, including the 2009-2013 American Community Survey 5-year Estimate, U.S. Census TIGER/Line Files, and 2000 Census Transportation Planning Package.

This analysis lets the Index estimate the yearly transportation cost for a specific area. CNT uses 15% of Area Media Income (AMI) as a threshold for transportation affordability. Combined with the standard 30% of AMI threshold for housing affordability, the Index presents 45% of household income to be an appropriate metric of location affordability. The Index also models vehicle-miles traveled in order to calculate greenhouse gas emissions.

Applications

The H+T Index’s model of affordability gives transportation planners a new way to think about the link between land use, travel behavior, and cost of living. By providing a more comprehensive view of the link between transportation and affordability, the Index can be useful in corridor planning and route alignment that best meets the needs of a population. This was put into practice in Chicago, where the Metropolitan Planning Council used H+T Index data as part of a bus rapid transit corridor selection analysis.

Housing professionals can also use the H+T Index. By clearly displaying the location efficiency of various census blocks, policymakers can easily identify areas in which to prioritize development and demonstrate importance the importance of transportation in land-use planning. Cities such as San Francisco, California and El Paso, Texas have used the H+T Index to rethink the way they approach affordable housing development.

Index Customization

In cases where the Index is not specific enough for a city’s needs, the Center for Neighborhood Technology has worked to create customized versions. CNT partnered with the Urban Land Institute to tailor the tool to the San Francisco Bay Area; Minneapolis-St. Paul; Washington, DC; and Boston. These custom versions of the Index present a more accurate picture of local affordability by including additional data on land use and housing costs. The Minneapolis-St. Paul Housing + Transportation Cost Calculator, for example, lets users input information for a specific household and compare it to neighborhood averages.