THE LETTERMAN COMPLEX - Presidio Trust

4 . 1 E N V I R O N M E N T A L C O N S E Q U E N C E S : A L T E R N A T I V E 1( S C I E N C E A N D E D U C A T I O N C E N T E R )• Whether the alternative would result in excessive parking supply which would compromise the TDMstrategies designed to encourage non-automobile modes, and potentially result in an increase in vehicle tripsto the site.4.1.7.1 ADDITIONAL TRAFFIC VOLUMESAlternative 1 would generate 4,560 external (i.e., to areas outside the Presidio) weekday daily vehicle-trips, and490 vehicle-trips during the p.m. peak hour (Table 16). Of the 490 p.m. peak-hour vehicle-trips generated byAlternative 1, the majority would be outbound (380 vehicles) from the Letterman Complex, while 110 vehicleswould be inboundOverall, the Mason Street Gate would experience an increase of 350 vehicles during the p.m. peak hour fromthe existing conditions, with Alternative 1 comprising 14 percent of this increase. Alternative 1 wouldcontribute the majority of the increase in traffic volume at the Gorgas Avenue Gate. The existing p.m. peakhourtraffic volume at this gate would increase by 510 vehicles, with the alternative comprising 61 percent ofthis growth. The existing traffic volume at the Lombard Street Gate would be increased by 400 vehicles duringthe p.m. peak hour, and 13 percent of this increase would be due to the new development within the complex.The existing p.m. peak-hour traffic at the Presidio Boulevard Gate would increase by 220 vehicles, withAlternative 1 contributing up to 36 percent of the increase (Table 17).4.1.7.2 IMPACTS ON INTERSECTION OPERATING CONDITIONSCurrently, during the p.m. peak hour, two of the study intersections operate at LOS C, four intersections operateat LOS B, and one intersection operates at LOS A (Table 4). Under Alternative 1, three of the studyintersections (Presidio Boulevard/Letterman Drive/Lincoln Boulevard, Mason Street/Marina Boulevard/LyonStreet and Doyle Drive/Marina Boulevard/Lyon Street) would operate acceptably at LOS C during the p.m.peak hour (Table 18). Three of the five studied intersections (Lyon Street/Richardson Avenue/Gorgas Avenue,Lombard Street/Lyon Street and Presidio Boulevard/Lombard Street) on the boundary or within several blocksof the Presidio would fail (have LOS D or worse) under Alternative 1 during the p.m. peak hour (Table 18).The poor operating conditions at these intersections reflect the increase in traffic volumes traveling to and fromthe Letterman Complex and other land uses at the Presidio via Lombard Street and Richardson Avenue.The following intersection improvements as described in mitigation measures TR-1, Lyon Street/RichardsonAvenue/Gorgas Avenue Intersection Improvements, TR-2, Lombard Street/Lyon Street IntersectionImprovements, and TR-3, Lombard Street/Presidio Boulevard Intersection Improvements, and illustrated inFigures 15 through 17 would improve the operating conditions at the intersections to acceptable levels ofservice:• Lyon Street/Richardson Avenue/Gorgas Avenue Intersection Improvements – Prior to reuse of the site, theintersection would be reconfigured to provide left turns from Richardson Avenue to Gorgas Avenue and leftturns from Gorgas Avenue to Richardson Avenue at two separate intersections (Figure 15). Theseimprovements would mitigate the a.m. peak-hour operation of the intersection of Lyon Street and RichardsonAvenue from LOS F to LOS D under 2010 conditions.• Lombard Street/Lyon Street Intersection Improvements – Prior to reuse of the site, the intersection would besignalized and the one-lane eastbound approach would be restriped to provide one left-turn lane and one142 L E T T E R M A N C O M P L E X