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HomeMy WebLinkAbout2022-02-04 ACHD Update MemoMary May, President Alexis Pickering, Vice-President Jim D. Hansen, 2nd Vice President Kent Goldthorpe, Commissioner Dave McKinney, Commissioner _____________________________________________________________________________________________________________ Ada County Highway District • 3775 Adams Street • Garden City, ID • 83714 • PH 208-387-6100 • FX 345-7650 • www.achdidaho.org February 4, 2022 To: The City of Meridian Jon Wardle Brighton Development, Inc. 2929 W. Navigator Drive, Suite 400 Meridian, ID 83642 From: Paige Bankhead, E.I. Assistant Traffic Engineer Ada County Highway District Subject: MPP21-0007/ H-2021-0075 Rackham East Subdivision Review of the updated analysis for Silverstone Way/Overland Road intersection ACHD reviewed and issued the staff report for Rackham East Subdivision on January 10, 2022. The Rackham East Subdivision originally proposed to use Rolling Hill Drive to access the development, however, the traffic impact study indicated that the additional traffic from the development on Rolling Hill Drive under the 2023 total traffic (full build out of the development) conditions exceeds ACHD’s acceptable thresholds for local roads of 2,000 daily trips. Therefore, as part ACHD’s action on Rackham East Subdivision, ACHD recommended the development to use Rolling Hill Drive to access the site, but restricted the development to Phases 1 and 2 and required that Rolling Hill Drive be restricted to right-in/right-out only at Overland Road. In response, the applicant proposed to restrict Rolling Hill Drive to emergency access only, which would divert all the site generated traffic to the Silverstone Way/Overland Road intersection. ACHD required that the applicant submit an updated analysis for the intersection, as well as the Silverstone Way road segment with the additional site traffic that would be diverted from Rolling Hill Drive to Silverstone Way. The applicant submitted the updated analysis on January 21, 2022 and it included 2 scenarios, one with access to Rolling Hills Drive restricted to right-in/right-out at Overland Road and the second with access only to the via Silverstone Way. The results of the analysis are shown below. The original traffic impact study did evaluate the intersection of Overland Road/Silverstone Way with dual southbound left turn lanes for the scenario where Rolling Hill Drive is restricted to right-in/right- out only on Overland Road, as it wasn’t in place at the time that the traffic impact study was prepared, however, it was included in the updated analysis. The addition of the second southbound left-turn lane adjusted the signal phasing in the updated analysis so that this movement (southbound left) was converted from permitted to protected only, as dual left-turn lanes should avoid permitted phasing. This also affects the operations of the intersection causing some lane groups to operate better or worse than before. The intersection operations improve overall in the updated analysis, however, some lane groups operate worse. The updated analysis shows that the southbound right- _____________________________________________________________________________________________________________ Ada County Highway District • 3775 Adams Street • Garden City, ID • 83714 • PH 208-387-6100 • FX 345-7650 • www.achdidaho.org turn movement and east-bound left-turn movements not failing as badly as before due to the phasing changes. However, the southbound left and westbound through/right movements worsen due to the phasing changes and additional traffic in the westbound right-turn movement. Staff supports the applicant’s proposal to restrict Rolling Hill Drive to emergency access only because the analysis shows that the intersection operations exceed ACHD level of service planning thresholds with and without the additional site traffic and the worsening operations mainly impact the Rackham development, who proposed this scenario, while improving the other lane groups operations. In addition, the intersection is built to its full configuration and there is not enough existing right-of-way for any additional improvements. It should be noted that an analysis for the intersection that includes the southbound left-turn lane under the 2023 total traffic conditions with access to Rolling Hill Drive as right-in/right-out only is estimated to operate only slightly better than the updated analysis which assumes no access to Rolling Hills Drive, but still would exceed ACHD’s acceptable level of service planning thresholds. This is because the additional traffic on Silverstone Way in the updated analysis is 143 additional trips in the AM peak hour and 157 addition trips in the PM peak hour, which is only a 12% and 9% increase respectively, which is not a large enough to result in significant changes in the operations of the intersection. The updated analysis also evaluated Silverstone Way. The original analysis with right-in/right-out access on Overland Road from Rolling Hill Drive projected a maximum of 1,084 PM peak hour trips, _____________________________________________________________________________________________________________ Ada County Highway District • 3775 Adams Street • Garden City, ID • 83714 • PH 208-387-6100 • FX 345-7650 • www.achdidaho.org which exceeds ACHD’s acceptable level of service threshold 1,080 peak hour trips for a 5-lane collector road. The updated analysis estimated 1,197 trips. However, this segment cannot be widened because it is a constrained segment, it is already built out to its full configuration and additional improvements are not feasible due to the limited right-of-way. Based on the updated analysis, staff is supportive of the applicant restricting Rolling Hill Drive to emergency access only for Rackham East Subdivision.