Even with market corrections bringing the cost of homes down in recessionary times, the United States remains in the midst of an affordable housing crisis. And a new study by the Chicago-based Center for Neighborhood Technology (CNT) illustrates just how bad it may be.

Some 48,000 American communities that are currently considered affordable to those making the median family income may actually not be affordable when you factor in the transportation costs necessary for homeowners to get to work, school, and the other locations that shape their daily lives. The study, “Pennywise and Pound Fuelish,” examined housing costs in 337 metro areas nationwide, which collectively are home to 80% of the U.S. population.

Historically, housing has been considered affordable when it claims 30% of the median household income or less. According to that formula, approximately 69% of American communities are considered affordable.

However, factor in transportation costs involved in living in these neighborhoods with lower home prices, and the share of communities qualifying as affordable drops by a third. That means that only two in five communities nationwide (39%) are truly affordable to those earning the median family income, per the revised metrics.

“The [current definition of affordability] does not take into account the almost equal cost of transportation, which can effectively double the cost of housing,” said Scott Bernstein, president of the Center for Neighborhood Technology, during a March 23 media briefing. Transportation costs can range from 12% to 32% of household income, he said, depending on the location.

To this end, CNT has parlayed the study data into a new interactive mapping tool that allows users to get ultra-granular in charting cost-of-living calculations by place. The Housing + Transportation Index contains data on 161,000 neighborhoods, allowing consumers, builders, and developers to pull up average housing and transportation costs for block-by-block comparisons. The architects of this new tool hope it will help home buyers and renters make more informed decisions about where to live, thereby avoiding the risky decisions and overleveraging of assets that lead to foreclosures.

“People have been moving away from central cores and employment … and now in a time of economic decline, we see people defaulting on their mortgages because they did not realize they were assuming a transportation cost burden along with their mortgage,” HUD deputy secretary Ron Sims said during the briefing. “We have also found that when people move away from jobs, they are often moving away from schools and other critical infrastructure, such as grocery stores, which means they have even more added costs getting to those places.  This index is long overdue, and we hope it will allow Americans to make better housing decisions by having more information.”

Home buyers aren't the only users who stand to benefit from the index, according to CNT officials. The tool is also intended to provide government with useful data upon which to shape policies and decisions about how and where to invest public funds.

“Transportation planning in the United States needs to be recalibrated so that the focus is broader than merely reducing traffic congestion,” Bernstein argued. “We are now realizing that the more we expand road capacity and encourage driving, the more we are contributing to cost of housing.”

“We need more mass transit, more car sharing, and more making land use count,” he said.  “If by 2030 we can reduce car ownership by even a quarter of a car per household, we’ll see $200 billion a year in consumer expenditure savings, even at current gas prices… which we expect will go up.”

Where home builders choose to build, and particularly where homes are sited in relation to transportation options, will matter greatly going forward--particularly for those seeking to offer homes that are affordable to average Americans.

“Transportation costs are now the second-highest household expense after housing,” said Nick Turner, managing director of the Rockefeller Foundation, which funded the research. “For many Americans, the only option is to drive, and that’s a hidden cost burden. We have crashed into our limits of 20th-century thinking, policies, and solutions. This is an issue that’s critical to the future survival of the middle class.”

Jenny Sullivan is a senior editor covering architecture, design, and land use for BUILDER. 

Learn more about markets featured in this article: Chicago, IL.