Louis Thompson Tightline
What's happening now
***Update*** One-Way Traffic Detour Resumes September 10
Traffic will switch back to one-way traffic up the hill on Louis Thompson Road beginning September 10, 2025 - October 30, 2025.
The contractor plans to install the detour after 8:30 AM the morning of September 10. Once the detour is in effect, all traffic will be directed one-way up the hill from East Lake Sammamish Parkway. After September 10, the one way closure is expected to be moved up the hill just past 205th Avenue NE.
Work During One-Way Traffic and Detour
Grading and concrete placement for driveway approaches begins this month on 9/15. Residents with driveways directly off Louis Thompson Road will be receiving flyers with specific dates and parking provisions during work and the following concrete cure time.
Curb, gutter and sidewalk construction is also underway with separate crews on construction of several retaining walls. This work phase severely narrows the travel lane, which necessitates the one-way traffic detour through final paving. Final paving is planned for October.
Traffic Impacts:
- One-Way Traffic Only:
Louis Thompson Road will be open to southbound (uphill) traffic only, 24 hours a day, from September 10 - October 30, 2025. - Closure to Northbound (downhill) Traffic: From 210th Place SE to 205th Avenue NE (near East Lake Sammamish Parkway), Louis Thompson Road will be closed to northbound traffic.
- Detour signs will be posted, and residents should use alternate routes to travel northbound. See Detour exhibit here.
- Access and Services Maintained:
- Southbound traffic will maintain access to all driveways and side streets.
- Vehicles exiting neighborhoods onto Louis Thompson Road must travel southbound (uphill).
- In coordination with the Lake Washington School District, all school bus routes will continue to operate with uphill-only routing.
- Garbage collection and mail delivery will continue without interruption.
We appreciate your patience and cooperation as we work to improve local infrastructure. Please plan ahead for possible delays and follow all posted signage and flagger directions during the detour.
Project Background
Louis Thompson Road is a vital connection route serving residents of Sammamish and surrounding communities. Historically, the corridor has been impacted by uncontrolled stormwater runoff. This construction phase will improve Louis Thompson Road from 210th Place Southeast to Eastlake Sammamish Parkway Northeast.
Following community feedback and preferences expressed previously, the City of Sammamish City Council approved the implementation of proposed alternative #4 in September 2022. Planned improvements include:
- Upgrades to existing stormwater conveyance, culvert, and ditch systems in the area to alleviate flooding, erosion, and landslide issues.
- A new sidewalk and bike lane on the north (downhill) side of the road to improve safety and connectivity to adjacent neighborhoods.
- A 6-inch paint line and widened 6-foot shoulder on the south (uphill) side to improve safety along the road.
Recent Photos
Project Needs and Goals
Controlling stormwater runoff and erosion
Uncontrolled stormwater runoff from the existing roadway and surrounding private properties results in erosion of the existing ditches and at culvert outfalls. Upgrades in the stormwater collection and conveyance system will be implemented to improve conditions and reduce the frequency of flooding events, erosion, and possibility of landslides.
Adding a sidewalk and bike lane
The corridor does not currently include any sidewalks, bike lanes, or other non-motorized improvements. While the project’s primary goal is to address the stormwater runoff issues, the City will also be adding non-motorized improvements, including a sidewalk and bike lane to connect adjacent neighborhoods with Lake Sammamish.
Protecting streams and wetlands
These improvements will be coupled with the City’s commitment to protecting environmentally sensitive areas, such as stream crossings and wetlands. The City will work with the community and appropriate agencies to ensure that roadway improvements are made without negatively impacting natural areas and areas which serve as important habitat for fish and wildlife.
Project Design
This project will upgrade the existing stormwater conveyance, culvert, and ditch systems in the area and alleviate the flooding, erosion, and landslide issues. New sidewalk and bike lane will improve safety.
Selected alternative
The preferred alternative - selected by City Council in September 2022 and informed by community input earlier this year – will include a sidewalk and bike lane on the north (downhill) side of the road, as well as a 6-in paint line on the south (uphill) side of the road. The south (uphill) side of the road will also be locally widened to provide a five-foot wide shoulder throughout the project area.
Project location
These improvements will be built from 210th Pl SE to Eastlake Sammamish Parkway NE. See the cross-section and map below for more details.
Outreach and Community Engagement
August 2024 - Virtual Public Meeting #3
Thanks to everyone who attended our Virtual Open House on Wednesday, August 7. A recording of the presentation and Q&A is available below.
October 2022 - Virtual Open House
Thanks to everyone who attended our Virtual Open House on Thursday, October 27. A recording of the presentation and Q&A is available below. You can also view the slideshow.
May 2022 - Virtual Public Meeting
Thank you to everyone who attended our May 5 Virtual Public Meeting. If you were not able to make it, you can view a recording of the presentation and Q&A below. You can also view the slideshow.
- The City is planning to engage the public throughout the design process to gather community input on proposed improvements and build trusting relationships with stakeholders.
- The City is committed to a clear and transparent design process to ensure the final design reflects the preferences of the community and meets their current and future needs.
- The City's project team is available to meet virtually with interested community organizations, schools, businesses, property owners, and residents to share more about the project and better understand concerns, priorities for design, and how they would like to communicate with the City and share input throughout the project.
The health and safety of the greater Sammamish community will be the forefront priority when planning and executing outreach related to this project. The project team expects to prioritize virtual and digital engagement opportunities for the foreseeable future.
Grant funding partners
- King County Flood Control District - Flood Reduction Grant: $700,000 (2022 and 2023 Awards)
- King County Flood Control District - Sub-Regional Opportunity Grant: $192,942
- Department of Commerce - State and Local Fiscal Recovery Funds: $3,000,000
