A month after the largest earthquake preparedness drills in Northwest history – “Cascade Rising” – I began wondering about the seismic preparedness of our transit systems, both current and proposed. I’ve written about transportation and natural disasters before, and though life-or-death situations rightfully make subway health the least of our worries, I do believe we have a moral duty not to assume that private vehicle access is a universal option in a crisis.
I asked Sound Transit’s Bruce Gray about their assets, mostly Link guideway (both elevated and tunneled). He responded in two parts, discussing the damage the system can take while still being operable, and the damage threshold that would cause the infrastructure to collapse or be fundamentally unsafe.
Gray said that the operational threshold is “a 150-year return period seismic event. If an earthquake like Nisqually happened again, Link could remain operational with minimal disruption as long as the tracks were clear and we were able to maintain power to the system.” In terms of structural safety, the design standard is a “2,500 year” standard, meaning that the systems are engineered to withstand the “Big One” that would destroy so much of our other infrastructure (including I-5)
It’s designed to avoid major failure and maintain life safety after the worst earthquake that experts can predict will happen every 2,500 years or so. Is this scenario Link would likely not be operational because of track blockages or power disruptions but the infrastructure would be standing. Backup systems would be able to power fire/life/safety systems in our underground stations but they would not be able to power the line.
In the news coverage of the drills, much focused on supply airlifts and strategies for rebuilding roads quickly to reopen access. Though these are critical of course, Link’s robustness should factor into disaster preparedness scenarios, too. If priority were given to restoring power to the line, freight and supplies could have a safe north-south artery on which to travel. Patients and officials unable to reach hospitals could reach temporary emergency facilities at UW. In any case, it’s good to know that what we’re building is resilient, even if we still have a long way to go as a broader community. Though feet and bicycles are the most resilient of all, we should think long and hard about the proper role for transit in natural disasters.