City engineering presented results of a traffic study for the Spyglass corridor on 116th Street and recommended installing a traffic signal at either Clubs Farm Boulevard or Spyglass Ridge Drive and building a two-way connection between Spyglass Falls and Spyglass Hills to improve left-turning movements and reduce crash risk.

The study, described by an Engineering Department staff member, analyzed five scenarios over a 10-year horizon using a 0.5% annual growth projection and evaluated queue lengths, level of service and intersection spacing. The presenter said the recommended near-term options were a signal at Clubs Farm Boulevard or a signal at Spyglass Ridge Drive and that a two-way connection between the neighborhoods would make any signal work more optimally.

“The best recommendations from the engineering department and our traffic consultant was to make a one-way connection at Laurel Falls Lane in Spyglass Falls, neighborhood ties into Knightsbridge Boulevard, one-way exit lane with a stop controlled at Knightsbridge Lane,” the Engineering Department staff said, and added the consultant estimated one proposed construction cost at about $3,450 for the one-way connection option (as presented in the study materials).

The study compared the no-build baseline with four signal-placement scenarios (Clubs Farm Boulevard, Sand Creek Boulevard, Spyglass Ridge Drive, and a scenario that combines a signal with elimination of a left turn from Spyglass Falls). Engineers reported that adding a signal increases queue length on 116th Street eastbound and westbound lanes but still produces levels of service the city finds acceptable (many intersections remained at level-of-service A or B in the study’s outputs). At some intersections, protected left-turn phasing would require a lead/lag arrangement to avoid conflicting left-turn movements.

The presenter also discussed queue-length constraints between adjacent intersections: about 570 feet between Clubs Farm and Sand Creek Boulevard and roughly 430 feet between Sand Creek and Spyglass Ridge Drive. The study modeled whether signal queues would back up into adjacent intersections and concluded the signal scenarios would not block neighboring intersections under the study assumptions.

Estimated construction costs varied by location. The presenter said a signal at Klutz/Clubs Farm would be in the roughly $520,000 range depending on market conditions; adding a signal at Spyglass Ridge Drive would add approximately one additional signal pole and equipment, increasing cost by roughly $100,000.

Board members and staff discussed tradeoffs including whether a signal placed at one intersection would primarily serve that immediate neighborhood unless the two neighborhoods were connected. Councilmember questions focused on safety and whether the signal would materially degrade 116th Street performance. Engineering staff said the new signal(s) would be tied into the existing signal system along 116th Street and could be coordinated to limit impacts.

Engineering staff recommended that either a signal at Clubs Farm Boulevard or Spyglass Ridge Drive would be effective and reiterated that a two-way connection between Spyglass Falls and Spyglass Hills would provide the greatest benefit; staff noted, however, that public feedback collected earlier showed resistance to building that connection.

There was no vote on any construction or funding action during the meeting. Staff said they would share the study materials with affected neighborhoods and return later with cost estimates and next steps if the council asks them to proceed.