A Sounder commuter rail extension to DuPont and bus rapid transit lines on State Route 522 and Interstate 405 are also part of the package.

[8] A second ballot measure, called Sound Transit 2, was proposed in 2007 to fund the deferred light rail segments left off the scaled-back system and further expand into the suburbs.

[10][11] The proposition was rejected, with the opposition campaign led by environmentalists (including the Sierra Club and King County Executive Ron Sims) who were concerned about the 186 miles (299 km) of new highway lanes and ramps that would have been built by the plan.

Light rail to Federal Way was truncated to South 200th Street in SeaTac, while the rest would be studied for a future expansion; East Link to Bellevue and Redmond was delayed to 2023 from 2021.

[24] The following month, the Sound Transit Board unanimously voted to pursue new taxes to support the 2016 ballot measure, pending authorization from the Washington State Legislature.

[33] Additional studies for provisional light rail lines between Ballard and the University District (via Fremont), West Seattle and Burien, and suburban extensions to Kirkland and North Everett.

[36][37] In response to the concerns over project timelines and routing choices, groups from Northwest Seattle and Snohomish County proposed alternative plans to better serve Interbay and Paine Field in Everett, respectively.

[38][39] In May 2016, Sound Transit announced revised plans that would accelerate delivery dates for light rail projects, pushing most into the 2030s, using an additional $4 billion in bonds that would not affect the taxing rate.

[48][54] Sound Transit 3 would extend Sounder commuter rail service to Tillicum (near Joint Base Lewis–McChord) and DuPont from Lakewood station, to open in 2036.

[67] The measure was also supported by several city councils in northern and eastern King County in the summer of 2016, including Bellevue,[68] Issaquah,[69] Kenmore,[70] Redmond,[69] and Shoreline.

[77] Sierra Club executive director Michael Brune argued that the package's projects would provide great benefits to the environment and addition of affordable housing near stations.

[79] The city councils of Newcastle and Sammamish passed legislation in opposition to Sound Transit 3, citing the lack of benefits to their respective communities.

[80][81] State representative Reuven Carlyle of Ballard published an editorial opposing the measure over its cost, putting education funding in jeopardy because of the use of property taxes.

[84] Bellevue city councilmember Kevin Wallace argued that a smaller plan to serve higher-density corridors with rail and others with bus rapid transit would be more cost effective.

The editorial board of The Seattle Times criticized the plan in June 2016 as coming "too soon" and too costly, calling it a "blank check" to Sound Transit.

[88] The plan has also been criticized for not promising to reduce congestion, with Sound Transit citing induced demand and touting light rail as an alternative rather than a solution.

[89] After the release of the draft plan in March 2016, including completion of light rail to Everett and Tacoma in 2041 at the earliest, politicians demanded shorter timelines that were eventually implemented.

[95] After the publication of the final plan and planning of the ballot measure language on voter pamphlets, a write-in campaign succeeded in placing conservative activist Tim Eyman on the committee writing the "no" statement, which upset the opposition campaign; under the state's ballot measure laws, Sound Transit's board were required to choose authors for both sides, and primarily selected current and former elected officials for both teams.

[97] The Washington State Attorney General's Office announced that it would not pursue legal action against Sound Transit for the incident, finding no evidence that the release was intentional.

[103] Work on implementation of the program's elements began in the following days, with Sound Transit approving preliminary engineering on light rail extensions to downtown Redmond and Federal Way, which were deferred in 2010 and included in the package.

[112] During the 2017 session, House Republicans attempted to move legislation allowing cities to exempt themselves from the Sound Transit district onto the floor, but were blocked by the Democratic majority, who were seeking to use their own MVET reform proposal.

[116] The Senate Law and Justice Committee conducted an investigation into the legislature's passing of taxing authority, with Republican members concluding that it had been unconstitutional and included misleading statements.

The investigation was dismissed by Sound Transit as a "partisan endeavor" and criticized by Democratic members of the committee over its secrecy and timing weeks before a special State Senate election.

[117] Anti-tax activist Tim Eyman attempted to file an initiative to cap the car tab fee at $30, but failed to collect the minimum number of signatures required for the November 2018 ballot.

Sound Transit estimated that the bill would reduce revenue by $780 million over the next 11 years, and also introduce indirect impacts to debt costs and project delivery schedules.

[120] To mitigate the financial impact, the Senate Transportation Committee proposed a $518 million exemption from sales taxes that would have been paid by Sound Transit into the education fund.

It was placed on the November 2019 ballot and was passed by 53 percent of voters, but its legality has been disputed; the King County Superior Court issued an injunction a few weeks after the election that halted implementation of the new MVET scheme.