西雅图的轻轨扩张以极高成本和工程复杂度推进，核心案例是跨越华盛顿湖一英里浮桥的I-90段，这是全球首个建在浮桥上的轻轨系统。该工程将高速公路两条车道改造为四节编组电力列车通行，依赖可旋转轨道支架与阴极保护系统，应对风浪位移与腐蚀风险。最新的2号线全长14英里，总投资37亿美元，2008年获批、原定2020年通车，目前仍在推进中。
整个Link系统自2009年首线开通以来进入多十亿美元级扩张期。1号线已延伸至41英里，仅最近两段北延和南延就分别耗资30亿美元和25亿美元。2016年通过的540亿美元税收方案计划新增62英里轨道，使系统最终达到116英里，按人均里程计为全美最大扩建。建设带动客流快速回升，2019年以来客流增长24%，2025年10月单月客流达340万人次，同比增加40万，成为美国轻轨中疫情后恢复最快的系统。
但成本与治理问题日益突出。机构面临约300亿美元的建设资金缺口，部分项目严重超支，例如7.7英里的Ballard线成本飙升至220亿美元，为最初预估的两倍。未来维护仍需额外50亿美元。尽管如此，税收收入占2026年预算的68%，为短期推进提供缓冲。安全方面，袭击事件从2023年的140起降至2024年的123起。随着2026年世界杯预计吸引75万名球迷，系统将在高峰时段实现四分钟一班的运行密度。
Seattle’s light rail expansion is advancing with exceptionally high costs and engineering complexity, highlighted by the I-90 crossing over Lake Washington, a one-mile floating bridge that hosts the world’s first light rail system of its kind. Two highway lanes were converted to carry four-car electric trains using rotating track supports and cathodic protection to manage wind- and wave-induced movement and corrosion. The latest project, the 14-mile 2 Line, costs $3.7 billion, was approved in 2008, and originally targeted a 2020 opening.
The broader Link system, which began service in 2009, is undergoing a multibillion-dollar growth phase. The north–south 1 Line now spans 41 miles, with recent northern and southern extensions costing $3 billion and $2.5 billion respectively. A $54 billion tax package approved in 2016 funds 62 additional miles, bringing the planned system to 116 miles, the largest US transit expansion on a per-capita basis. Ridership has risen 24% since 2019, reaching 3.4 million monthly riders in October 2025, a 400,000 increase year over year and the strongest post-pandemic recovery among US light rail systems.
Costs and governance remain major challenges. Sound Transit faces an estimated $30 billion construction shortfall, with some projects doubling in price, including the 7.7-mile Ballard line at $22 billion. An additional $5 billion is projected for maintenance. Still, 68% of the 2026 budget is backed by local taxes, providing near-term stability. Safety incidents declined from 140 assaults in 2023 to 123 in 2024. With an estimated 750,000 fans expected for the 2026 World Cup, the system plans four-minute peak service, putting its capacity and reliability under global scrutiny.