The Center for Housing Policy, an affordable housing group, has a new report out called A Heavy Load: The Combined Housing and Transportation Burdens of Working Families, that's worth a look. Following up on earlier research by the Center that shows "a clear trade off between the housing and transportation costs of Working Families" (note the capitalization), the report shows that while working families in the 28 metropolitan regions studied spend about the same percentage of income on housing as most families (27.7% for working families against 27.4% for all households), their transportation costs are nearly 50 percent greater.

There are some methodological problems here, particularly in the study's definition of working families as those with annual income between $20,000 and $50,000, without adjusting for pay variations between regions. And of course the report is intended to push a chronic affordable housing crisis.

Still, it's striking how little variation there is in combined housing and transportation costs between regions, with working families spending an average of 57% of total income on housing and transportation (against 47.6% for all families), ranging from 54% in Pittsburgh to 63% in San Francisco. There are much greater variances in the housing-transportation split, with St. Louis at 23-32 at one end, and chronic outlier San Francisco at 35-27 at the other.

The Center pushes the claim that apparently affordable housing is often illusory, with all savings and then some eaten up by car and commuting costs. The data doesn't seem to go quite as far, but there's an excellent point at the end of the article linked above—"A three-car family puts a lot of money into depreciating assets, instead of into mortgages and college educations."