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San Joaquin County Community Environmental Setting,Impacts,and Mitigation Measures Development Department Transportation and Traffic For this analysis,both a 10-year and a 20-year design period is used for calculating TI's. The Caltrans method of calculating TI described in the Highway Design Manual(Caltrans 2000,in Omni-Means 2005)was used as the basis after determining the ESA-L. Separate TI values were developed for the improvements to SR 132 as part of the SR 132/Bird Road Interchange Project. These separate TI values include the truck loads anticipated for the proposed project and are,therefore,not considered in this analysis. The design of County roads in the project area was reviewed and is discussed below. Bird Road A review of the Bird Road Improvement Plans(1997,in Omni-Means 2005) indicated a TI value of 8.5 was used in designing the structural section along southbound Bird Road,and a TI value of 10.5 was used in designing the structural section along northbound Bird Road. The lower TI value was used for southbound Bird Road because the majority of trucks are traveling empty in this direction and are significantly lighter than the loaded northbound Bird Road trucks(Omni-Means 2005). Koster Road A review of the County's "Road Inventory" indicated Koster Road is built on six-inches of base material that has been sealed over the years. Though the actual structural section on Koster Road is unknown at this time,the existing structural section should be based,as a minimum,on a 10-year TI value of 9.0 calculated based on existing daily traffic volumes assumed to remain constant for l0-years along this segment of Koster Road(Omni-Means 2005). Blewett Road A review of the County's "Road Inventory"indicated that Blewett Road is also r built on six-inches of base material that has been sealed over the years. Approximately 100-feet of Blewett Road at the approach to Bird Road was reconstructed when Bird Road was improved. Though the actual structural r. section on Blewett Road is unknown at this time,the existing structural section should be based, as a minimum, on a 10-year TI value of 9.0 calculated based on existing daily traffic volumes assumed to remain constant for 10-years on Blewett Road just east of Bird Road(Omni-Means 2005). Baseline Traffic Index Values Table 3.L-13 presents the calculated TI values on Bird Road,Blewett Road and Koster Road just south of the DeSilva Gates quarry entrance for existing(10-year TI value),and year 2007 baseline(10-year TI value)traffic conditions. The calculated TI does not differentiate between loaded trucks traveling one way on the study area roadways with empty trucks traveling the opposite direction (Omni-Means 2005). r DeSilva Gates Quarry Project Draft Environmental Impact Report 31-13 J&s 05105.05