The funding for the agency is through a pair of US DOT programs; the Transportation Infrastructure Finance and Innovation Act (TIFIA) and the Railroad Rehabilitation & Improvement Financing (RRIF) program. The loans will finance Sound Transit projects in the greater Seattle metro area, which also includes the cities of Bellevue, Tacoma, and Everett, and covers urban areas of the state's three most populated counties. 

Sound Transit is a previous recipient of significant TIFIA loans with $3.84 billion, DOT’s largest loan package to date, awarded for six projects in 2021 and another $658 million lent in 2018.

"US DOT's $327 million in loans to support Sound Transit’s light and commuter rail lines supports an alternative to car travel on congested roadways and improve(s) connections to jobs, healthcare, and educational opportunities," said US DOT Secretary Polly Trottenberg in a statement. "These three new projects will reduce carbon emissions and improve air quality."

Sound Transit has earmarked the funds to extend its light rail system line by 2.4 miles, build new stations, purchase new light rail vehicles, improve bike, parking, and pedestrian infrastructure, create new bus and paratransit facilities, expand an operations and maintenance facility, and improve access to the system for commuters. 

Funding  includes two TIFIA loans in the amounts of $93 million and $73 million, supporting Sound Transit's Hilltop Tacoma Link Extension and its Elevated Light Rail Platform Along Lynnwood Link Extension projects, respectively. The RRIF loan of $154.2 million is for the agency's commuter rail Sounder Access Improvements project. The loans cover 33-49% of each individual project.

According to Sound Transit, the loans will save taxpayers at least $26 million over the next two decades.

"These loans are an important federal investment in our shared commitment to build the regional transit network that will fuel future success," said Sound Transit Board Chair and King County Executive Dow Constantine.  

The interest rate on TIFIA and RRIF loans is equal to the rate paid by the U.S. Treasury to borrow for a similar period on the date the loan is approved. The rate on 30-year municipal treasury bonds is 3.45% at the time of this writing. Sound Transit estimates that the loans will save $245 million through 2046 when the agency's voter-approved expansion plan is expected to be completed, and a total of $445 million over the entire life of the three loans.

Sound Transit Board Chair and King County Executive Dow Constantine said, "Strong partnership with the federal government is crucial to our success, and these loans signal a shared commitment to reinvest in the nation's infrastructure and help us build the transit network our region needs."

According to DOT, the department has supported more than $133 billion in infrastructure investments through the TIFIA financing program, closing more than $38.9 billion, and $7.6 billion through the RRIF program.

Independent of other local transit agencies, Sound Transit operates three transit services, including Link in Seattle and Tacoma, Sounder commuter rail, and the 28-stop Sound Transit Express bus system. The agency is primarily funded by local sales, property, and motor vehicle excise taxes, and is governed by an eighteen-member Board of Directors made up of elected officials from member jurisdictions and the Washington State Board of Transportation.