Modernizing Mitigation: A Demand-Centered Approach (SSTI, September 2018)

Cities exist to provide people and firms with access to goods, services, employment, and other people. A mark of a city’s success is the clustering of complementary land uses to residents’ and businesses’ mutual benefit; the more people and activities within reach of each other, the greater the benefit from this accessibility.
A problem arises, however, when cities try to address transportation impacts from such clustering. Conventionally, they estimate the motor vehicle trips from a proposed land use in a popular location—often exacerbating the number of trips through requirements for off-street parking—then require the new land use to “mitigate” the resultant traffic impact through roadway capacity increases, either directly or through in-lieu or impact fees.
The conventional approach has significant problems, including:

  • Placing expensive burdens on desirable new land uses, possibly pushing them into less-accessible locations—often places that non-auto travelers reasonably cannot reach.
  • Inducing more traffic and the resulting environmental, safety, livability, and personal cost problems.
  • Reducing the ability of travelers to use non-auto modes because of impediments posed by wider, busier roadways.

In short, the conventional approach degrades the accessibility of cities, undermining their fundamental ability to function.
This report proposes a new approach to assessing and responding to land use-driven transportation impacts, called “modern mitigation.” Instead of relying on auto capacity improvements as a first resort, this approach builds on practice around transportation demand management (TDM) to make traffic reduction the priority. Based on programs dating to the 1990s in several cities, a modern mitigation program requires certain new land uses to achieve TDM credits through such means as:

  • Improving area walking, biking, and transit infrastructure and service.
  • Providing complementary land uses that minimize the need for travel.
  • Subsidizing transit, or bikeshare or carshare services.
  • Providing first- and last-mile connections to high-capacity transit.
  • Implementing monitored TDM measures of their own design.

The program as described here provides benefits to the community from reduced impacts of traffic and travel costs, as well as to such particular stakeholders as incumbent land uses, developers and building owners, and staff members administering programs.
The program is described as a function of local government, with requirements triggered by building permits and/or land-use permission changes. However, it may also be adapted by states for use in mitigation they require of land uses that affect the state highway system.
Download the full report.