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Per City of Santa Ana requirements, the ICU calculations use a lane capacity of 1,700 vehicles per hour (vph) for through lanes and 1,600 vph for left -tum lanes and right -tum lanes. A clearance adjustment factor of 0.05 was added to each Level of Service calculation. Per City of Tustin requirements, the ICU calculations use a lane capacity of 1,700 for through and all tum lanes. A clearance adjustment factor of 0.05 was added to each Level of Service calculation. The ICU value translates to a Level of Service (LOS) estimate, which is a relative measure of the intersection performance. The ICU value is the sum of the critical volume to capacity ratios at an intersection; it is not intended to be indicative of the LOS of each of the individual turning movements. The six qualitative categories of Level of Service have been defined along with the corresponding ICU value range and are shown in Table 3-I. 3.3.2 Highway Capacity Manual (HCM 6) Method of Analysis (Unsignalized Intersections) Two-way stop -controlled intersections are comprised of a major street, which is uncontrolled, and a minor street, which is controlled by stop signs. Level of service for a two-way stop -controlled intersection is determined by the computed or measured control delay. The control delay by movement, by approach, and for the intersection as a whole is estimated by the computed capacity for each movement. LOS is determined for each minor -street movement (or shared movement) as well as major -street left turns. The worst side street approach delay is reported. LOS is not defined for the intersection as a whole or for major -street approaches, as it is assumed that major -street through vehicles experience zero delay. The HCM control delay value range for two-way stop - controlled intersections is shown in Table 3-2. 3.3.3 Level of Service Criteria According to the Cities of Santa Ana and Tustin, LOS D is the minimum acceptable condition that should be maintained during the peak commute hours. However, the City of Santa Ana has defined exceptions to this criterion at specific locations within the study area. The City of Santa Ana has defined major development areas where LOS `B" is considered acceptable. Caltrans "endeavors to maintain a target LOS at the transition between LOS "C" and LOS "D" on State highway facilities"; it does not require that LOS "D" (shall) be maintained. However, Caltrans acknowledges that this may not always be feasible and recommends that the lead agency consult with Caltrans to determine the appropriate target LOS. Caltrans has determined that all state owned facilities that operate below LOS D should be identified and improved to an acceptable LOS. The Caltrans Traffic Impact Study Guidelines dated December 2002 does state that if an existing state owned facility operates at less than LOS D, the existing service level should be maintained. Based on the above, the following summarizes the LOS required for each key study intersection: 75B-75