Laserfiche WebLink
City of Santa Ana <br />August 31, 2023 <br />Page 2 <br />Traffic Operations Comment 2: No maximum saturation flow rate (Veh/hr) per <br />single lane for any movement should exceed 1800 (veh/hr). However, ATTACHMENT <br />I APPENDIX E FROM REVISED TRAFFIC CIRCULATION ANALYSIS FOR THE <br />RELATED BRISTOL DATED JUNE 2023, shows the following: Intersection 30: <br />Bristol Street at I-405 NB Ramps, Scenario 1: 1 AM Existing shows 1863 (Veh/hr) for <br />the Bristol Street Southbound Right/Through shared lane. Recommended <br />improvements should be addressed in the Memorandum prepared by Linscott Law & <br />Greeenspan Engineers on August 16, 2023. Intersection 31: Bristol Street at I-405 SB <br />Ramps, the saturation flow rate (veh/h) for the Bristol Street Southbound right lanes <br />movement is not provided. Please provide missing information. <br />Response to Comment 2: The comment states that no maximum saturation flow rate <br />per lane for any movement should excess 1800 vehicles per hour (veh/hr). In LLG's <br />history of more than 50 years, to our recollection, this is the first time that we have <br />received a comment by Caltrans requesting that we use anything other than a starting <br />saturation flow rate of 1900 veh/hr per lane and then allowing for adjustments as <br />necessary, including recent projects where Caltrans was a reviewing agency. <br />In addition, as part of our third party peer reviews of other traffic consultants traffic <br />studies performing LOS/Queuing assessments for Caltrans ramp facilities, this same <br />methodology/approach is adhered to. From our experience, the use of saturation flow <br />rate of 1900 vph/hr per lane is a practical and common industry wide approach. <br />Further, the Caltrans Guide for the Preparation of Traffic Impact Studies (December <br />2002) does not specify saturation requirements for analysis, and therefore a starting <br />saturation flow rate of 1900 veh/hr per lane appropriate, which is consistent with the <br />suggested default saturation values identified within the current Highway Capacity <br />Manual (HCM). <br />Nevertheless, a comparative analysis has been prepared using the two different <br />saturation rate assumptions (1800 veh/hr vs. 1900 veh/hr) at the study intersection of <br />Intersection No. 30 - Bristol Avenue at I-405 NB Ramps for existing traffic <br />conditions. The results of this assessment are summarized in Table B. As shown, the <br />results of the sensitivity assessment indicate that the change in saturation flow (i.e. <br />using 1900 veh/hr) would yield a nominal decrease in intersection delay (LOS). <br />N:\4400\2214410 - Bristol Commons - CONFIDENTIAL, Santa Ana\Report\4410 Caltrans Response Memo 8-31-2023.docx <br />