The Center for Neighborhood Technology has a Housing and Transportation Affordability Index which

provides a more comprehensive way of thinking about the true affordability of place. It presents housing and transportation data as maps, charts and statistics for 917 metropolitan and micropolitan areas—covering 94% of the US population. Costs can be seen from the regional down to the neighborhood level.

The recent focus on combined housing and transportation costs is very useful when planning affordable housing policies as total housing and transportation costs provide a better guide to housing cost burden than housing costs alone.

The Housing and Transportation Affordability Index

shows that transportation costs vary between and within regions depending on neighborhood characteristics:

• People who live in location-efficient neighborhoods—compact, mixed-use, and with convenient access to jobs, services, transit and amenities—tend to have lower transportation costs.
• People who live in location-inefficient places—less dense areas that require automobiles for most trips—are more likely to have higher transportation costs.

The traditional measure of affordability recommends that housing cost no more than 30% of household income. Under this view, a little over half (55%) of US neighborhoods are considered “affordable” for the typical household. However, that benchmark fails to take into account transportation costs, which are typically a household’s second-largest expenditure. The H+T Index offers an expanded view of affordability, one that combines housing and transportation costs and sets the benchmark at no more than 45% of household income.

When transportation costs are factored into the equation, the number of affordable neighborhoods drops to 26%, resulting in a net loss of 59,768 neighborhoods that Americans can truly afford. The key finding from the H+T Index is that household transportation costs are highly correlated with urban environment characteristics, when controlling for household characteristics.

A lot of housing policy rests on the definition of affordability, whether it is that housing cost should be no more than 30% of household income or that housing and transportation costs should be no more than 45% of household income. It would be useful for researchers to take a fresh look at those benchmarks to ensure that they make sense in today’s economy.