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9611 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7600
Fax: 206.276.7663
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City of Mercer Island / City and Regional Projects / Sound Transit Park-and-Ride

Sound Transit Park-and-Ride

The Mercer Island Park-and-Ride is located at 8000 N. Mercer Way. 

Sound Transit Park & Ride Location Map - click for online map

Sound Transit Rider Information

Metro Bus Trip Planner

The Sound Transit Park-and-Ride Project on Mercer Island opened in early 2008 and includes a two-story parking garage at the previous Mercer Island park-and-ride lot site. The garage is owned and operated by Sound Transit and provides 447 parking stalls on two levels, increasing the capacity of the previous lot by approximately 200 stalls. Improvement to the bus boarding areas along North Mercer Way doubled their capacities, and provided new bus shelters, bicycle lockers, lighting, and signage. Additional project amenities include CCTV surveillance, landscaping, public art, and bike routing.

On most weekdays the Park-and-Ride is full by about 7:00am. To learn about reaching the Park-and-Ride by foot, bicycle, or bus, view the transportation alternatives and trail map from King County Metro's Mercer Island In Motion campaign.

Click here for 2015 user data, based on license-plate surveys

Parking Alternatives

Click here for information on other MI Park-and-Ride locations (operated by King County Metro)

Click here for information on Metro's pilot TripPool program that provides free commuter vans and a free RESERVED parking space at the Park-and-Ride.

Click here for information about possible future expansions to Island commuter parking (as part of the preparations for regional light rail).

Click here for information on the City's street-parking permit program for residents.


Park and Ride Ownership

The City of Mercer Island has never owned the Park-and-Ride property. In 1987, it was sold by a private owner directly to WSDOT when construction for the I-90 widening project (launched 1982) was fully underway.

A smaller, single-story Park-and-Ride facility was constructed on the property in the mid-1980's, after 10 years of study by WSDOT and King County Metro Transit.

When parking expansion plans were approved by the voters, the property was purchased in 2005 from WSDOT for $1.5million by Sound Transit. The City was not offered any opportunity to buy the property.

Today, Sound Transit operates the expanded facility, which serves both Sound Transit and King County Metro Transit buses.

Park and Ride Historical Background

In 1996, Mercer Island voters supported Sound Move, a regional transportation plan that created Sound Transit’s Regional Express Bus service. Sound Transit’s project proposed adding 230 spaces on Mercer Island as part of a trio of I-90 related improvements on the Island.

Sound Transit has worked through the I-90 Project Steering Committee to identify a preferred location for a park-and-ride facility they will build on the island. The Mercer Island City Council recommended the south of I-90 underground facility as its preferred park-and-ride location in November of 1999, which recommendation was supported by the Steering Committee.  The estimated cost of that alternative, $13.8 million for one floor of parking and $22 million for two floors, significantly exceeded the project budget of $13.3 million.

Up until January of 2001, Sound Transit treated the I-90 roadway improvements, park-and-ride, and transit station as a combined project. However, decision-making on an I-90 Center Roadway configuration has proven complex and time-consuming. In an effort to advance a park-and-ride solution, in December the City Council asked Sound Transit to “decouple” the park-and-ride and transit station parts of the project from the decision on the I-90 roadway configuration. Sound Transit agreed to do so.

In January 2001 Sound Transit summarized the estimated costs for an underground parking structure at the preferred location and concluded “(T)he project budget cannot support a project like this.” At the same time, the letter restates Sound Transit’s commitment to building additional park-and-ride spaces on Mercer Island, and the intent to work with the City to “explore alternatives.”

In March of 2001, the Council directed the City Manager to explore the possibility of other options, specifically the opportunity to develop some sort of public-private partnership with new developments planned in the Town Center. Staff was asked to look into whether additional public parking for Mercer Island residents could be added to the Island Market Square property project at approximately SE 27th Street and 78th Avenue SE and/or to the project planned for the property at approximately SE 27th Street and 77th Avenue SE

In summer 2002, a private developer, Dollar Development, proposed an option in which they would construct an additional 200 parking spaces to be used as park and ride spaces.  Sound Transit staff worked with the developer to evaluate this option.


In September 2002, the Sound Transit Executive Committee directed staff to continue developing the Dollar Development option and to build cost information for comparison purposes.


Sound Transit’s preliminary analysis by geo-technical, structural, transportation and parking design consultants compared the advantages, disadvantages and the cost of constructing 200 park and ride spaces at the proposed development with the cost of constructing 200 underground spaces and with adding 400 above-ground spaces at the existing Mercer Island park-and-ride lot located on North Mercer Way.  The analysis found that:

  • Dollar Development’s current design of the park and ride spaces is tight and has reduced maneuverability.  Redesign may be required to meet Sound Transit’s circulation requirements.  There may be a cost impact.
  • Dollar Development’s design would locate Sound Transit park and ride spaces on two separate floors, about 1200 feet from the existing transit center.
  • Access control to prevent use of park and ride spaces by non-transit users has not been addressed in the design concept.
  • Structurally Dollar Development’s design can be modified to accommodate an additional floor of parking.
  • Adding 200 trips to the traffic analysis for this site is not a fatal flaw.  The environmental analysis (SEPA) for the site would need to be amended.
  • Per stall costs for the proposed Dollar Development option and an underground parking option at the existing site are similar.  However, Sound Transit policy rules out the incrementally higher cost of underground parking spaces at any park-and-ride lot it is constructing.
  • The per stall cost of two floors of above-ground parking at the existing site is still the most cost-effective option of providing more park and ride spaces on Mercer Island however, Mercer Island staff and council are opposed to this option.

The proposed concept had potential benefits to Sound Transit and Mercer Island.  It was hoped that it would provide an opportunity to meet Mercer Island’s park-and-ride needs at a potentially reasonable cost.  The site would require a longer walk to access transit service, but it is within industry standards for acceptable walking distances to transit.  Sound Transit staff has identified functional requirements for the park and ride spaces including location of spaces at street level closest to bus access, consistency with Sound Transit and ADA design standards, access control, security, maintenance and hours of operation.  Sound Transit would acquire the park and ride spaces through a condominium type arrangement which would include some property rights and control in the facility.  The arrangement would be structured as a turn-key agreement in which Sound Transit would set forth specific requirements and Dollar Development would commit to providing them for a maximum price, with a defined schedule.


Sound Transit staff updated their Executive Committee on the status of negotiations in December, 2002.  There was an inability to close the gap between the $26,500 per parking stall cost identified by Dollar Development and the $19,000 per stall cost set by Sound Transit. 

Consequently, this public/private development option was abandoned.


As part of their preliminary design efforts, Sound Transit collected the following data to assist with interim parking and transit operations during reconstruction of the park-and-ride lot.  To accommodate the number of Mercer Island transit riders during closure of the existing lot, Sound Transit plans to lease additional park-and-ride spaces south of I-90. Sound Transit also collected numerous comments and suggestions. 

Existing Use of Mercer Island Park-and-Ride and Bus Stop (2002)



Daily (weekday)

Total # of Boardings


Total # of Parking Spaces


# of Parking Spaces Used




The number of boardings is more than 3 times the number of available parking spaces, suggesting that a large number of transit riders are walking to the transit stop, being dropped off, or parking elsewhere on the Island, in addition to a small number of transfers.


Table 2 provides information on the origin of the users of the Mercer Island Park-and-Ride, based on license plate information. [Click here for 2015 user data based on license plate surveys.]


Table 2

Origin of Users of Mercer Island Park & Ride (2002)



Number of Users

Mercer Island


I-90 Corridor East of Mercer Island


I-405 Corridor South of I-90


Other widely dispersed








During 2003 Sound Transit evaluated three options to add 200 additional park and ride spaces to the existing North Mercer Way lot on Mercer Island. They included:

  • Add one floor above grade
  • Build a “daylight basement” with parking depressed ½ floor below grade
  • Add one floor below grade

Sound Transit staff recommended the daylight basement option, in which the lower park-and-ride floor would be depressed about one-half of a floor and would take advantage of the existing varying grade on the site.  This option reduces the visual impacts of the additional park-and-ride lot spaces.


There was a significant level of backing for this approach on the part of Mercer Island City Councilmembers.  City Council support was predicated on Sound Transit’s use of the daylight basement approach in order to reduce overall impacts on adjoining neighborhoods.


At the same time, the Council instructed City staff to plan for additional neighborhood parking restrictions around the park-and-ride lot by creating a Residential Parking District.  Under such a district, only residents and their guests would be allowed to park along neighborhood streets during regulated hours.  An ordinance forming such a district was introduced and ultimately approved by the Council in November 2003.


The Sound Transit Executive Committee directed their staff to proceed with the daylight basement concept at the existing Mercer Island park-and-ride.


A critical component of Sound Transit’s initial planning was to develop a relocation plan to address the park-and-ride lot needs during construction.  In addition, new environmental processes that were not anticipated when the original Mercer Island Park-and-Ride/Transit Center scope was first compiled had to be completed as part of the scope.  These included preparation of a biological assessment, endangered species analysis, additional stormwater analysis, development of three alternative aesthetic concepts, public review of the concepts, parking structure ventilation and security, and replacement parking and transit service access during construction.



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