Present laws require air quality modeling for all projects within or affecting a non attainment area for criteria pollutants as established in the National Ambient Air Quality Standards (NAAQS). Projects must have emission projections below the NAAQS limits. Where documentation requirements call for an environmental impact statement on the project, an air quality study is required regardless of the project's location.
The basic model requirements include the roadway alignments and the volumes and speeds for roadways. Plans must show locations near the project that are accessible to the general public such as sidewalks, residences, parks, playgrounds and even vacant lots. Plans must be 100' to 1" scale, 50' to 1" or 1:1000 (metric). The travel lanes and roadway widths must be easily discernible. Plans for all alternatives must be current and should not have changed significantly since the project's submittal to the regional metropolitan planning organization for inclusion in the transportation improvement program (TIP). Only TIP and project level modeled alternatives can proceed to the construction phase.
Include traffic volumes, speeds and intersection data for roadways immediately adjacent or substantially influenced by the project. Traffic data may include intersections outside the project limits. Provide complete data for each alternative, including the no build alternative, and for existing year, opening year and horizon year (2030 for the Puget Sound Regional Council area), however, horizon year may differ within different jurisdictions. The Air Quality specialist will determine the horizon year for the local air quality agency in the project area. Data should include all existing signalized intersections and those proposed for signalization under the project. The submittal must include the specific information described below to model intersections. For further information contact the air quality specialist.
Data Requirements at Signalized Intersections:
The following information is essential for input to the CAL3QHC computer model:
- Cycle Length of the signal in seconds;
- For each movement at the intersection, include the following information; Volume; Number of lanes; Red Time ( green time minus cycle length).
Placing this information in a format, such as the one below, is helpful to ensure an accurate and efficient entry into the computer model.
Intersection of 114th Avenue S. ans SB State Route 567 off ramp |
The air quality computer model allows the user to input optional parameters. The use of optional parameters can markedly increase the accuracy of the air quality study when program assumptions differ substantially from those used by the department. Designers should supply this data whenever possible. The following are the optional parameters allowed by the air modeling program:
- Clearance interval lost time,
- Signal is actuated, semi actuated, pretimed;
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Arrival Rate:
- Platoon arrives at beginning of the red phase,
- Platoon arrives during the red phase
- Random arrivals,
- Platoon arrives during green phase,
- Platoon arrives at the beginning of the green phase,
- Saturation flow rate.
Show all metered ramps. Include the metering rate, queue length and show which lane is metered if the ramp has more than one lane. The traffic data should include the effects of ramp metering on mainline volumes and ramp speeds.
Projects, each having a unique nature, may require additional information. Please contact Mia Waters at 206.440.4541 with any questions.
Projects having a unique nature, may require additional information. Please contact the Air Quality Staff for questions.