Abstract:Hot-spot [localized carbon monoxide (CO) and particulate matter (PM10) violations] analysis is often required by the Environmental Protection Agency (EPA) to determine project level air quality conformity of transportation projects in accordance with state implementation plans. EPA uses intersection level of service (LOS) as one of its major criteria for identifying potential CO hot spots. EPA's 1992 "Guideline for Modeling CO from Roadway Intersections" states that hot-spot analysis is not required for those intersections operating at LOS A, B, or C (i.e., these intersections are automatically eliminated as potential CO hot spots), whereas intersections operating at LOS D or worse must undergo detailed CO concentration analysis. Of all possible LOS D intersections, clearly only a few will actually require detailed modeling of CO concentrations. A new screening methodology that introduces the concept of meteorological situation-orientated reference charts is presented. Variations on the basic reference charts can incorporate such effects as signal type (e.g., pretimed versus actuated) and future fleet characteristics. Once the desired reference charts have been developed, to use them the analyst needs only to identify the applicable reference chart on the basis of the location of the project at hand and an approximate background concentration. The proposed screening methodology should save both effort and money often wasted on the redesign of intersections that are predicted to be hot spots at the time of air quality conformity analysis and when detailed air quality analysis of LOS D intersections is undertaken for intersections that are unlikely to be CO hot spots.