Seattle First Hill Streetcars out of service

2½-block skid has Seattle scrutinizing streetcar safety
Originally published March 11, 2017 at 7:00 am Updated March 11, 2017 at 2:01 am

A train skidded last week on the First Hill line — a risk the city must address there, and on the future First Avenue streetcar near crowds of pedestrians, to open in 2020.

The momentary loss of power from a low-voltage battery was enough to send a Seattle streetcar skidding down Broadway on its rails for 2½ blocks, a safety hazard that technicians are still trying to cure several days later.

Though nobody was injured, the incident March 1 disabled four kinds of braking methods on the streetcar — and explains why city transportation chief Scott Kubly, citing an abundance of caution, is keeping the entire First Hill line closed.

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The problem with relays is that they are mechanical systems with moving parts, and moving parts all eventually fail. The streetcar had one of these controlling the braking systems, and it failed. That’s not unusual; what is unusual is that it exposed a major design flaw in the streetcar: all of the braking systems were controlled by the same load contactor. That’s called a “single point of failure” and it’s a big no-no in electrical systems design — especially critical systems like brakes.

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