FHWA sought to update its 2000 to 2004 PM research plan (Carr et al., 2002a) to reflect recent scientific findings and to anticipate information needs for the 2005 to 2010 time period. The 2005 to 2010 time period complements the long range PM research portfolio prepared by the National Research Council (National Research Council, 1998).
Preparation of this Strategic Plan completes the third of a three-step process FHWA initiated to update its 2000-2004 PM research plan. The first step of FHWA's effort was to commission an assessment of recent and ongoing PM research and to identify important research gaps (Tamura et al., 2005) . The second step was to convene approximately 50 national experts to evaluate the PM assessment document, identify additional research issues, and reach consensus on high-priority PM research issues. The consensus-building process occurred at a one-day workshop held on April 7, 2005, in San Diego, California. Workshop participants included environmental and transportation planners from state and regional DOTs and MPOs; and representatives from air quality agencies, industry, the academic community, and consulting organizations. Workshop findings were documented in a Workshop Summary report (McCarthy et al., 2005) .
The main contribution of FHWA's effort has been to achieve broad consensus across a wide range of stakeholder groups that four transportation-related PM research issues are of highest priority for the 2005 to 2010 time period. High-priority research issues include
In addition to the high-priority research needs, the work has also identified a variety of medium and lower priority research needs.
Members of the MPO-DOT community expressed that, among these additional research needs, several research efforts that could be completed in the near-term were especially important. These include
FHWA intends to work with its partner agencies and with other stakeholders to provide funding or other forms of support for these priority research efforts. Completion of these research efforts will advance understanding about the relationship between on-road mobile sources and PM problems, provide improved analysis tools for SIP and conformity analyses, and facilitate identification and implementation of effective PM control strategies.