The transportation conformity rule establishes project-level analysis requirements that apply in carbon monoxide (CO) nonattainment and maintenance areas. These include a requirement for quantitative CO hotspot modeling at all locations affected by a proposed project operating or expected to operate at a Level of Service D or worse. Transportation agencies, aware of declining ambient CO levels and lower idle emission factors in MOBILE6, are concerned that this is no longer an efficient use of their limited resources. A summary is provided of project-level screening procedures developed and adopted by transportation agencies throughout the nation, several innovative practices are highlighted, and recommendations for developing refined screening protocols are offered.