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MOUNTAIN HOUSE PROPOSED ALTAMONT HEIGHTS TENTATIVE MAP 4. ENVIRONMENTAL CHECKLIST 4.15 TRANSPORTATION TRAFFIC The SPIIIEIR analyzed segments of arterial.roadways and freeways as,well as key intersections following buildout of the Mountain House Community in 2025-The 2025 peak- hour LOS,on arterial:streets before and after implementation of traffic in`rtigation measures recommended in the MEIR and approvals associated with Neighborhoods E F.and G were presented in the SPIIIEIR(EDAW,2005b,Table 4.11=15). The a nalysis'revealsthal most of the segments would operate at an acceptable LOS even without mitigation. Traffic impacts on these segments would therefore be less than significant.' Roadway widening is needed to 'maintain acceptable LOS in some segments. With implementation of the mitigation measures,only the segment of Altamont Pass west of Grant Line Road remains at LOS F. Following mitigation,the following segments would have LOS D: • Byron Road east on Grant Line Road during the afternoon peak-hour. f" Grant Line Road east of Mountain House Parkway during the afternoon peak-hour. i • Grant Line'Road east of Byron Road during the morning and afternoon peak-hours. The current traffic computer model projects a peak-hour traffic demand of approximately 21,000 vph along Tracy/Mountain House corridor of I-205 in 2025. The freeway would not be able to accommodate all.the projected demand in one hour,and the projected traffic could only be realized through peak spreading(i.e., spreading the traffic out over more than one hour). Most segments of 1- 580, 1-205, and I-5 north of 1-205 are expected to be over their capacity,operating at LOS F(EDAW, 2005b). This is a significant and unavoidable impact, with or without the proposed project. As commute traffic on highway facilities reaches congested levels, commuters begin to change their travel patterns by either finding less congested routes or commuting during off- peak hours. Already, some traffic leaves the freeways and travels along parallel roadways such as Von Sosten Road, Grant Line Road, and Byron Road in the Specific Pian III area and Altamont Pass Road further west of the Specific Plan III area(EDAW, 2005b). The 2025 morning and afternoon peak-hour LOS for 50 intersections (assuming the proposed I-205/Lammers Road interchange is not constructed) are presented in of the SPIIIEIR (EDAW, 2005b,Table 4.11-16). The data in the table is based on the assumption that the improvements in the MEIR and the approvals for Neighborhoods E, F and G, as well as the Grant Line Road improvements proposed in Specific Plan lII, have been implemented. No intersections would have a LOS F. The following intersections would operate at LOS D: i • Grant Line Road/Altamont Pass Road during morning and afternoon peak-hours. • Mountain House Parkway/Byron Road in the afternoon. • Byron Road/Henderson Road in the morning. Great Valley Parkway/Byron Road in the afternoon. All these intersections would require traffic signal control(EDAW, 2005b). All the Mountain House streets would be built to accommodate projected traffic generated by build-out of the Mountain House Community and other planned developments in the area. I 4-76