Transportation conformity regulations require an evaluation of the impact of transportation projects on the concentration of particulate matter less than 10 microns in aerodynamic diameter (PM10). As of early 2005, the U.S. Environmental Protection Agency (EPA) had not released quantitative assessment guidance; thus, the conformity regulations require only qualitative PM10 evaluations. In December 2004, EPA published proposed regulations to revise the PM hot spot analysis requirements. The proposed regulations include various PM10 and PM2.5 analysis requirement options, but do not yet include or reference guidance materials needed to complete such analyses. Absent analysis tools and guidance on how to conduct quantitative analyses, which is largely due to the complexity of the primary and secondary nature of PM10 problems, project analysts have struggled to determine project level impacts on localized PM10 concentrations. This report describes a new protocol for qualitatively analyzing project-level PM10 effects to determine whether a transportation project will create a PM10 “hot spot” problem. The protocol was developed by the UC Davis-Caltrans Air Quality Project at the University of California, Davis (U.C. Davis) on behalf of the California Department of Transportation (Caltrans) and the U.S. Federal Highway Administration (FHWA). The protocol includes a four-part methodology to screen projects unlikely to contribute to exceedances of the PM10 air quality standards: (1) a “project comparison” approach for maintenance areas that allows users to compare the proposed project to pre-existing facilities, (2) a “project comparison” approach for nonattainment areas, (3) a “threshold screening” analysis that takes advantage of real-world measurements of the contribution of roadways to observed PM10 concentrations, and (4) a “relocate and reduce, build vs. no-build” approach that assesses whether a project will spatially reallocate traffic to reduce hot spot problems. Project analysts can use the protocol as a resource to comply with the transportation conformity regulations.