Air Quality Conformity

The US Environmental Protection Agency (EPA) sets air quality standards, known as National Ambient Air Quality Standards (NAAQS).  Areas where monitoring shows that these standards are not met are said to be in “non-attainment”.  Within Clark County, the Las Vegas Valley has been designated as a non-attainment area for carbon monoxide (CO) and for particulate matter less than 10 microns in diameter (PM10).  PM10 is more commonly known as dust.  A larger area, comprising about 60 percent of Clark County, is in non-attainment for ozone.

Transportation plans and programs in non-attainment areas are subject to a process known as air quality conformity.  Under this requirement, RTC must quantitatively assess the air quality impacts of its plans and programs.  In particular, RTC needs to demonstrate that changes in the transportation system will not cause the areas to exceed motor vehicle emissions milestones set by the EPA and the local air quality agency.  The local air quality agency, Clark County Department of Air Quality (DAQ), also develops implementation strategies to ensure that milestone emissions levels are not exceeded.

These milestone levels and implementation strategies are set out in a series of State Implementation Plans (SIPs).  DAQ has prepared SIPs for CO and PM10 and has submitted an early progress plan for ozone.  In order to conduct the transportation conformity analysis, RTC uses a travel demand model.  This computer program uses estimates and projections of population, employment, and transportation infrastructure information.  The outputs from this model are used to analyze the air quality impacts of future transportation projects based on various parameters from an air quality model.  These parameters generally consist of the milestone levels set by the SIPs and the air quality model.  The following are links to the information that make up the factors for the travel demand model:

Land Use by Traffic Analysis Zones (Clark County Comprehensive Planning)

Population Forecasts (Center of Business and Economic Research at UNLV)

Employment Data (Nevada State Department of Employment, Training, and Rehabilitation)

Traffic Counts (Nevada Department of Transportation)

Appendix 3 of the Regional Transportation Plan FY 2009 – 2030: Planning Variable Development and Methodology

Appendix 4 of the Regional Transportation Plan FY 2009 – 2030: Travel Demand Model Methodology and Air Quality Conformity