Our regional light rail system has expanded a lot in the past year, and we know the transformation has also meant growing pains at times for some of our passengers—whether it’s crowded peak-hour trains and parking garages or scheduled service disruptions to prepare for opening seven more stations in 2025 and 2026.
In the last four months, we’ve also seen a significant uptick in unplanned outages on both the 1 and 2 Lines.
A variety of recent issues have reduced or disrupted service entirely. Causes include signal malfunctions, leaky valves on light rail cars, and power outages.
Out of 6,500 hours of total service we’ve provided this year through late November, we’ve had 376 hours of reduced or disrupted service.
In other words, service has not been up to our (or your) standards roughly 6% of the time. And while all large rail transit systems experience some degree of unplanned outages and planned maintenance, this 6% is not acceptable to us.
In response, we recently launched a comprehensive, systemwide analysis into these issues with our Link operating partner, King County Metro. And while our assessment isn’t finished yet, we want you to know what we’ve learned so far, and what we’re doing about it.
What we’ve learned so far
There’s still a lot we’re working to understand through our analysis of these service disruptions, which we began this summer and fall and will continue into January. But our findings so far have helped us pinpoint some important issues.
In reviewing our service interruption data, we’ve found that most fall into one of three causal categories:
1. Issues with Series 2 light rail vehicles: Our newest vehicles have been experiencing several mechanical problems, including leaks, valve control problems, and hydraulic fluid contamination within the braking systems.
These are performance issues, not safety concerns, but they can lead to (usually short) service interruptions. These vehicles are also having various issues in their communication systems, like malfunctions in passenger information displays and in rear-view mirrors.
2. Signal malfunctions within the train control system: If one signal is out or not working properly, we stop operations through that segment to ensure safety until we can inspect and resolve the issue.
In recent weeks, we’ve specifically seen an increase in signals flagging “false presences” on the tracks – essentially alerting operators and our Link Control Center that a train exists where it doesn’t. This can happen through debris on the rails, excess ballast (gravel and rock) adjacent to the tracks, and other reasons. In the case of one such interruption last week, crews were able to adjust the pad and materials underneath the track to resolve the signal problem.
3. Electrical outages in the traction power system: Just as in your home, excess or stray electrical current can cause issues that “trip the breaker,” or in this case our traction power substations. The substations are designed to cut power when this occurs for safety reasons, but it’s the existence of excess/stray current that we are working to eliminate.
We’ve also identified some issues with the connections between the overhead catenary wires that power the trains, including incorrect tension and electrical arcing.
As you can see in the graph above, the most common incidents, related to light rail vehicles, are generally the quickest to resolve, with an average of 34 minutes.
That’s often because our Link Control Center can immediately deploy “gap trains” to get passengers back on their way quickly and get the vehicle in question back to the shop for maintenance.
By contrast, failures in the traction power system are the least common type of disruption, but they can cause more lengthy delays (six hours on average) when they happen. We’re working diligently to both reduce the occurrence of these outages and improve the speed with which we’re able to resolve them.
There are a lot of components to this electrical system, including traction power substations (or TPSS, located throughout the system); the overhead catenary system (or OCS, the network of wires that draw electricity from the TPSS); pantographs (which look like antennae on top of light rail vehicles, connecting to the OCS); and the return current from the rails to the TPSS units. Given that complexity, diagnosing and solving traction power issues can sometimes take hours.
Now that we have a clearer understanding of the three main issues affecting service, we’ve also been able to identify some immediate actions to improve reliability within the next few weeks. These simple interim fixes include things like:
Train operators coasting (not accelerating) through areas with recent known power issues without reducing train speeds or affecting the train’s schedule.
Adjusting the OCS wire tension throughout the downtown Seattle tunnel as necessary to improve the contact quality and reduce the risk of power outages.
Using a vactor truck to clean the rails in the tunnel to reduce stray current impacts on the system.
King County crews are gearing up to execute these repairs immediately, starting in December and heading into the new year.
And what comes next after that?
Enter: the tiger teams.
A multi-pronged approach
As Sound Transit and King County Metro staff shared with the Rider Operations and Experience committee on Dec. 5, we’ve established four “tiger teams” to continue exploring root causes, recommending solutions, and planning near- and long-term projects, beginning in April 2025 through Jan. 2026. We expect these four teams, composed of experts in multiple technical areas, to continue identifying more quick fixes as they go, too.
The four tiger teams will focus on:
Light rail vehicles: assessing and correcting issues with the Series 2 fleet.
Traction power and train control: identifying immediate repairs and near-term improvements to increase the reliability of electrical and signaling systems.
Comprehensive system review: a full analysis of the operating system to identify any structural vulnerabilities and near- and long-term solutions.
Passenger support and outreach: improving communications when disruptions occur.
Between now and January, these teams will be wrapping up their initial assessments and executing some quick fixes.
Working with King Country Metro staff, we’ll develop a systemwide, comprehensive plan by the end of March, and we’ll update the Sound Transit Board and the public again on our progress. Throughout the rest of 2025 (and likely into early 2026), we’ll be implementing the solutions we identify.
This urgency is driven by our commitment to improve passenger experience while also ensuring system readiness as we prepare to open three new 1 Line stations and four new 2 Line stations. The end result will be a much more resilient system you can fully rely on for daily use, as well as a system that can readily manage major public events such as the FIFA World Cup in summer 2026.
We aren’t taking these challenges lightly. You deserve service that’s consistently clean, safe, and dependable, and we’re committed to doing what it takes to get there.
Stay tuned for more updates and sure to sign up for rider alerts via email or text so you never miss a service update.