Like a drunk uncle at a family funeral, transportation projects in major cities tend to air out a community's normally hidden dirty laundry. In the abstract, it is hard to dispute the value of an efficient intercity mass transit system. But when a light rail or subway project threatens to change the landscape of long-inhabited neighborhoods, the impacts become more mixed. Gentrification, regional job opportunities, poverty, housing, and traffic all become part of the discussion.

Last week, the Pew Charitable Trusts released a report that illustrates the complexity of these questions. Pew and the Robert Wood Johnson Foundation funded a study by a trio of community organizations--an in-depth health impact study of a light rail line being constructed in the Twin Cities, Minnesota.

The summary is here.
The technical report is here.

The Central Corridor Light Rail Line is an 11-mile transit system connecting downtown Minneapolis with downtown Saint Paul. It is a $1 billion investment that is expected to spur $6.8 billion in local development over the next 20 years.

It is difficult to summarize the results of the study except to say that the health outcomes of the rail project vary. There are health benefits associated with the increased access to grocery stores and doctors' offices that mass transit provides, not to mention easier job commutes. Economic development through increased customer flow and employment opportunities also boosts the health of residents. Yet there are health risks associated with the accompanying rise in housing costs as low-income residents struggle to meet rent and utility increases. Moreover, residents with lower educations might not qualify for the newly created jobs that will require at least some college-level skills.

The study concluded that a commitment to affordable housing would help mitigate the negative impacts of the new rail system. The Saint Paul City Council took that into account when it approved the proposal, creating an affordable housing working group and commissioning feasibility studies.

Are there accepted rules of thumb about how transportation impacts peoples' health? What are the most important health benefits of mass transit? What are the biggest health dangers of mass transit? Can we ask similar questions about road projects? Is it worthwhile to engage in detailed (and costly) health impact analyses? If so, when are such studies appropriate?