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To learn about Sound Transit's current and planned projects explore the new System Expansion interactive map. This website is no longer being updated.


We compiled a list of frequently asked questions. Click on a question below to expand and read the answer. Want to dig deeper? Visit the Document Library for ST3 Plan documents.

  • The Sound Transit 3 measure will be decided by voters within the Sound Transit District, or more formally the Central Puget Sound Regional Transit Authority (RTA) District. This is the area where RTA taxes are collected and where the Sound Transit services they support are provided. The district includes the most populated areas of King, Pierce and Snohomish counties. Use the address locator tool to find out if your home address is within the district boundary. 

  • ST3 would complete major mass transit extensions every few years over a 25-year period. To learn about specific project times, view the project phasing factsheet.  

    ST3 recognizes that travelers in our region face increasing travel time challenges right now. ST3 includes an Early Deliverables Program that establishes relief in key corridors while longer-term projects are planned and constructed. The program includes, but is not limited to: Bus Rapid Transit (BRT) on I-405/SR 518 and SR 522/Northeast 145th Street; light rail extensions to Federal Way and downtown Redmond; capital investments on Metro’s RapidRide C and D lines to bring earlier improvements to Ballard and West Seattle; capital investments to increase bus speed and reliability on Pierce County routes and on Madison Street in Seattle; pursuing opportunities to run buses on highway shoulders as permitted; and additional parking and access improvements throughout the system.  Read the plan for more information about when projects are scheduled for completion.

  • Major infrastructure projects require significant time to plan, design and build. Variables can include lengthy environmental review and coordination with local jurisdictions. The Puget Sound region’s high level of existing development and its challenging geography and geology further add to project complexity and timelines.

    Due to these factors, planning and building major light rail projects typically takes 12-17 years, and longer for projects that are particularly complex due to design, construction and permitting challenges, such as the extensive underground construction through downtown Seattle for extending light rail to Ballard. Other ST3 projects, such as light rail extensions to Federal Way and Redmond, have already completed environmental review and will be ready to open in eight years. Watch a video to learn more about project delivery.

  • Transit is a primary tool used by regions around the world to add transportation capacity, particularly in the many situations where there is little room for expanding roads. While a freeway lane moves as few as 700 cars per hour and in ideal conditions up to 2,000 cars per hour, a four-car light rail vehicle can move up to 16,000 people per hour in each direction (4-car trains every 3 minutes). 

    One four-car train carries the same number of passengers as about 10 buses.  Moving the same number of people on buses would require 200 drivers and 200 buses competing for space on roadways that are experiencing greater congestion each year, even in HOV lanes. 

  • Light rail expansions will increase the people-moving capacity of our transportation system. Every rider is someone who does not contribute to rising congestion, helping to ease the movement of drivers and freight on our roads. However, when additional road space becomes available, whether by building new highway lanes or by moving people out of cars into transit, freed up capacity quickly fills with cars, a phenomenon known as induced demand. 

    Due to rising population, congestion will very seldom reduce from today’s levels, but without mass transit, it would be worse. Light rail offers an alternative to driving that also helps promote a vibrant and dense urban development where people rely less on cars, benefitting all travelers as well as our environment.

  • The Sound Transit Board of Directors shaped the ST3 Plan through more than two years of public involvement. Participation was very strong, particularly in April 2016 when Sound Transit received 2,320 written comments and 34,706 online survey responses, 40 percent more than the 2015 online survey. In addition, more than 1,250 people attended the seven open houses in April. The agency received more than 90 letters from local jurisdictions, agencies and stakeholder organizations. Public interest in transit investments was also reflected in a scientific telephone phone survey fielded in April.

    ST3 timeline graphic

  • Mass transit will continue to be critical to moving large numbers of people over long distances, particularly during peak hours. There will always be constraints on how many vehicles, automated or standard, can fit into the region’s most congested areas. It all boils down to space, which dense and growing cities inherently lack.

    Mass transit can be highly complementary with fleets of fully automated vehicles as they become feasible.  Self-driving cars could provide improvements to last-mile connections between transit centers and local destinations. At this point the timeline for fully-automated (including completely unoccupied) cars is uncertain and will require the resolution of numerous policy issues.

    ST3 includes an Innovation Fund to study and prepare for changing transportation technologies, such as self-driving cars and shared car services.

  • Parking investments are assumed to be part of many ST3 projects. In shaping plans for expanding the regional transit system, Sound Transit looks closely at options specific to each area served, working to emphasize opportunities for people to access transit through walking, bicycling and local transit connections, while making parking investments in areas where other access modes are more challenging. On the interactive map, parking would increase at stations where the letter “P” appears inside the circular symbol. Detailed assumptions can be founded by clicking a project to read its summary.

  • While the passage of ST3 would commit Sound Transit to serve the areas shown on the map, the precise locations of stations and alignments is determined through environmental processes that emphasize opportunities for public involvement. The lines on the map reflect the representative alignments that were used to develop estimates of ridership and costs. Read more about the typical project lifecycle through which the projects would be developed. 

  • Of Sound Transit 3’s $53.8 billion total budget, about half, or $27.7 billion would be funded by new taxes that voters will consider in November. These are: (1) a sales tax of 0.5 percent ($.50 on a $100 purchase) in addition to the 0.9 percent currently collected; (2) a motor vehicle excise tax (MVET) of 0.8 percent ($80 annually per $10,000 of vehicle value) in addition to the 0.3 percent MVET Sound Transit is collecting through 2028; and (3) a property tax of 25 cents for each $1,000 of assessed valuation. See more information about costs, including individualized tax calculator.

  • Rigorous independent oversight along with demanding internal cost and project controls help ensure that Sound Transit spends taxpayer dollars wisely.

    The discipline that has helped Sound Transit deliver major projects such as University Link and Angle Lake extension on or ahead of schedule and on or below budget, will continue through ST3. This includes oversight by a 15-member Citizen Oversight Panel and locally-elected Sound Transit Board members, as well as regular audits by state and federal government agencies and independent private-sector firms, including Deloitte, KPMG, Moss Adams, Booz Allen Hamilton and others. 

    Since 1994 Sound Transit has undergone 171 audits by state, federal and independent private sector auditors. This puts Sound Transit among the most heavily-audited agencies in the state.