Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration
Office of Planning, Environment, & Realty (HEP)

Qualitative PM10 Hot Spot Analysis

(extracted from the US 93 Supplemental Environmental Impact Statement, Ninepipe/Ronan Improvement Project, Lake County, Montana)

The qualitative analysis follows the March 2006 EPA/FHWA guidance, "Transportation Conformity Guidance for Qualitative Hot-spot Analysis in PM2.5 and PM10 Nonattainment and Maintenance Areas." The guidance requires that PM10 hotspot analyses address the following elements:

Section 93.123(b)(1) of the conformity rule only requires PM hotspot analysis for "projects of air quality concern", which are generally defined as projects which feature a large volume of diesel traffic. However, this provision does not apply in Montana; the state of Montana conformity requirements are based on an older version of the federal transportation conformity rule and do not reflect this provision. Thus, PM hotspot analyses are required for all non-exempt federal projects in Montana's PM10 nonattainment and maintenance areas, and the question of whether this project would be considered a "project of air quality concern" is not relevant. Section 93.123(b)(1) of the federal rule will only apply in Montana once the state of Montana conformity requirements have been revised to reflect the most recent federal requirements, and this revision has been approved by EPA.

Description of project (location, design and scope; date project is expected to be open)

This information is included in Part 1 (Summary) of this SEIS, with more detailed discussion in other sections of the SEIS. The differences in project design under the various alternatives are discussed in Part 3 of the SEIS. The PM hotspot analysis covers only the preferred alternative; if some other alternative is ultimately selected, that alternative will need to comply with the PM hotspot requirement and other project-level conformity requirements prior to issuance of a Record of Decision.

Description of existing traffic conditions and changes resulting from project

This information is included in chapters 4.1 and 5.1 of the SEIS.

Contributing Factors: Air Quality, Transportation and traffic conditions, Built and natural environment, Meteorology, climate and seasonal data, and Adopted emissions control measures

Much of this information is provided in other sections of this SEIS, including section 4.7 (air quality, meteorology, and climate data), sections 4.1 and 5.1 (transportation and traffic data), and sections 4.2 and 5.2 (built and natural environment). The above factors would be largely the same regardless of which alternative is selected, except that roadway configurations and travel speeds would change. Traffic volumes are not expected to change if the project is built. Ronan does not implement any control measures for PM10.

Five emission source categories of priority air pollutants in the project area were identified in the US 93 Evaro to Polson FEIS. These include automobile exhaust from vehicular traffic on roadways, residential heating (typically wood burning), agricultural activities, and road construction. These sources are still active today and industrial sources may be an additional source of emissions (Wahl 2003). Vehicular traffic also generates fugitive particulate emissions by causing small particles of soil and winter sanding material on the roadway to become suspended in the air.

Ronan is a Tribal nonattainment area. No state implementation plan has been developed for the area. The most recent comprehensive air quality emissions inventory for the area was conducted in 1991. This inventory indicated that approximately 80 percent of the PM10 emissions in Ronan were attributable to on-road mobile sources.

PM10 air quality is monitored in Ronan Park. There have been no exceedances of the PM10 standard at this station for the period 2002-2006; the last recorded exceedance was in November 1999. One exceedance per year is allowed under the PM10 standard, so compliance is based on the second highest value. As can be seen from the table below, recent second high values in Ronan are around one third of the 150 microgram per cubic meter PM10 standard.

Year Readings 1st Max 2nd Max 3rd Max 4th Max
2002 226 55 53 52 46
2003 226 58 52 50 47
2004 159 66 49 48 44
2005 53 61 56 36 33
2006 46 55 48 38 37

Description of analysis method chosen

This analysis uses the "monitor comparison approach" outlined in the March 2006 EPA/FHWA guidance. Under this approach, an air quality monitor is identified that has similar traffic volumes, truck activity and surrounding sources and land use as those in the project area, and PM10 monitored air quality from this comparison monitor is used to evaluate the likely PM10 conditions in the project area.

FHWA reviewed calendar year 2005 air quality and traffic data in two nearby communities where PM10 is monitored (Kalispell and Missoula). 2005 was chosen as it is the latest year for which traffic counts have been published. The monitor locations were identified, and then traffic counts on nearby streets were summarized. The comparison is discussed in more detail below.

This comparison assumes that truck travel fractions are the same on all comparison roadways. Complete truck percentage data were not available as part of the SEIS or for the comparison locations. MDT's 2005 traffic flow map shows that the truck percentages on US highways in Ronan, Kalispell and Missoula are roughly similar, and it was assumed that truck percentages on local streets would also be similar. The one exception is the Missoula Health Department monitor; this monitor is near I-90, which has a much higher truck percentage. Overall, since vehicle exhaust, brake and tire wear emissions are a very small fraction of total PM10 emissions (road dust is by far the major component in Ronan, making up 99.7 percent of total roadway emissions), the assumption that truck percentages are similar would not have any meaningful impact on the monitoring data comparison.

The comparison also assumes land use is similar in the three monitoring locations, when in fact Ronan has a smaller population and correspondingly less development and activity near the monitor than Kalispell or Missoula. The nearby community of Polson also monitors for PM10, and has land use that is more comparable to Ronan. However, the traffic volumes in Polson are lower than those expected in 2030 in the Ronan area, which prevented use of this monitoring site to evaluate the potential PM10 impacts of the projected traffic volumes in Ronan.

Description of type of emissions considered in the analysis (e.g., exhaust, road dust, construction emissions)

This hotspot analysis includes all sources of direct mobile source emissions, including road dust, tailpipe exhaust, brake and tire wear emissions. The conformity rule only requires consideration of construction emissions in cases where construction activity lasts longer than five years at any individual location, which is not the case for this project.

Description of analysis years

The conformity rule and the EPA/FHWA guidance require that PM hotspot analyses 1) cover the entire timeframe of the area's regional transportation plan, and 2) be based on the year or years in which peak emissions are expected. Ronan is not covered by a metropolitan planning organization and has no regional transportation plan. The air quality analysis for the project was designed to cover the timeframe of the recently-updated TranPlan 21 statewide transportation plan, which has a horizon year of 2030.

In order to identify the year or years of peak emissions, both mobile source trends and trends in background emissions need to be considered. The regional PM10 air quality analysis described in the previous section demonstrates that 2030 is the year of highest emissions from roadways in the nonattainment area. The contribution of background concentrations to total local PM10 concentrations is unknown, so these concentrations were assumed to be constant over time. National control programs to control fine particulate will tend to reduce transport of PM10 into the nonattainment area, but population growth in western Montana will tend to increase background PM10 over time. Therefore, it was concluded that 2030 represents the year of peak emissions.

Professional judgment of impact

As noted above in the regional air quality analysis, the traffic volume on US 93 in Ronan in the expected year of peak emissions (2030) is projected at 31464 vehicles per day. In the monitor comparison approach, FHWA compared this projected traffic volume to current (2005) traffic volumes and PM10 levels in Kalispell and Missoula to determine whether 31464 vehicles per day were likely to lead to a violation of the PM10 standard.

Monitoring data for the Kalispell and Missoula PM10 monitoring sites were obtained from EPA's AirData web site. Maps of the monitor locations were obtained from Montana DEQ, and traffic volumes near the monitors were determined by reviewing MDT 2005 traffic volume maps. The traffic volumes affecting the monitors are summarized in the following table.

Location/Nearby Streets Volume Total Volume
Kalispell (Flathead Electric)    
US 93 16830  
US2 28940  
4th Ave 6000  
Woodland Ave 3190  
2nd St 4460 59420
Missoula (Boyd Park)    
US 93 29260  
Russell St 15020  
Brooks St 23880  
Fairview Ave 4370  
Ernest Ave 930  
South Ave 14400 87860
Missoula (Health Dept.)    
I-90 21850  
Broadway 14140  
Spruce St 5970  
Higgins Ave 14770  
Orange St 16770  
Ryman St 2440 75940

Next, these traffic volumes for 2005 and the 2005 2nd maximum PM10 values were compared to the estimated 2030 traffic volume for US 93 in Ronan.

Monitor Location City 2005 2nd max PM10 2005 Traffic Impact 2030 Projected Traffic
Flathead Electric Kalispell 78 59420  
Boyd Park Missoula 58 87860  
Health Department Missoula 52 75940  
Ronan Park Ronan 56   31464

The monitor locations in Kalispell and Missoula are impacted by much higher traffic volumes than those expected in Ronan in 2030. At the same time, each of these monitor locations is currently measuring PM10 values well below the 150 microgram per cubic meter standard. Therefore, since these higher traffic volumes do not appear to be contributing to violations of the PM10 standard at the Kalispell and Missoula comparison monitors, the lower traffic volume of 31464 vehicles per day in 2030 would not be expected to cause or contribute to a violation of the PM10 standard in Ronan.

In addition to the monitor comparison, there are other factors that contribute to FHWA's conclusion that the project would not be likely to lead to violations of the PM10 standard. First, the regional emissions analysis shows that mobile source PM10 emissions are likely to increase by approximately 40 percent over the timeframe of the air quality analysis. This emissions increase will tend to increase PM10 concentrations over time. However, since current PM10 air quality values at the Ronan monitor are around one third of the PM10 standard, emissions could theoretically almost triple before the area would be at risk of violating the standard.

Also, the design features of the project will tend to reduce PM10 concentrations immediately adjacent to the roadway compared to the No-Action Alternative. The couplet design effectively cuts traffic volumes in half on the affected segments, which will result in lower PM10 concentrations along the central portion of US 93 compared to the No-Action Alternative. Other design elements that will reduce PM10 emissions compared to the No-Action Alternative include surfacing shoulders, adding curbs and gutters, and consolidating and surfacing gravel and dirt approaches. The PA will also pave 1st Avenue SW, which currently has minimal pavement.

Conclusion on how project meets 40 CFR 93.116 and 93.123

FHWA concludes that the preferred alternative will not cause or contribute to a violation of the PM10 standard for the following reasons:

  1. Monitors in other communities near Ronan are impacted by much higher traffic volumes than those associated with the peak year of the US 93 project in Ronan, and are not violating the PM10 standard.
  2. Current PM10 values in Ronan are approximately one-third of the PM10 standard, and emissions are not expected to increase enough to lead to a violation.
  3. The preferred alternative includes design features that will reduce dust trackout and emissions compared to the No-Action Alternative.
Discussion of any mitigation measures; written commitments for mitigation

As noted above, the preferred alternative is not expected to cause or contribute to violations of the PM10 NAAQS. Part of this conclusion is based on the mitigating effects of dust trackout controls. The project includes commitments for design elements that will reduce PM10 emissions, including surfacing shoulders, adding curbs and gutters, and consolidating and surfacing gravel and dirt approaches. The PA will pave First Avenue SW, currently with minimal pavement, as the southbound couplet. These commitments for design improvements are enforceable under section 93.125 of the conformity rule and the Administrative Rules of Montana (ARM 17.8.1402).

Updated: 7/6/2011
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000