The case for Automated Light Metro Technology for Ballard and South Lake Union

Sept. 2020 rendering of 160 Street Station on the Surrey-Langley SkyTrain Extension. (TransLink)

ST3 passed enthusiastically in the Seattle region because voters were excited to get mobility improvements. However, Sound Transit has had trouble coming up with compelling designs to deliver on this promise. To address this problem, we should revisit some of the design assumptions.

Vancouver's SkyTrain and Montreal's REM took far less time to design and construct. We can learn from them and adopt automated train technology. If Sound Transit would interline trains in the existing tunnel and keep the Ballard to Westlake line separate, the new line could use different technology.

Automated Light Metro

To accommodate the current 4-car trains a Link station has to be straight and level for 600 feet, 400 for the station and 200 for its approaches. This makes station placement challenging, in particular at grade, as it is more than a block. At the end of a line you also have to provide another 400 feet for a crossover before the station and another 400 feet for a tail track for a total of 1400 feet of straight track.

With automated trains you can get the same capacity by running trains of half the length at twice the frequency. As you don't need a cab, the trains still provide greater capacity. Shorter trains mean that the station is much easier to site. It requires less land acquisition and fewer utility relocations leading to cheaper and faster construction. In some cases the station could straddle the intersection without impacting existing adjacent buildings.

As tunneling has become more automated, tunneling cost is mostly driven by station construction. If the station footprint is smaller, the construction time, cost and carbon footprint become smaller, too.

As you don't have to accommodate a driver switch, you can pull into and out of the station at the end of the line far more quickly which may even allow you to build single-track end stations. In general, it makes branching into stub lines much easier.

Automated trains allow for longer operating hours, too. It allowed Copenhagen to provide 24X7 operations.

Mode Selection History

In 2014 Sound Transit studied various transit technologies with a focus on the Tacoma to Everett spine. They compared various rail, bus and other technologies like monorail, Maglev, people movers, gondolas and automated trains. They eliminated some from consideration as they could not meet the needs of regional transit. Others, like Maglev and automated trains, were eliminated because they require full grade separation. However, after the at-grade related issues in Rainier Valley, Sound Transit has focused on building grade-separate transit. We should revisit this decision given the report emphasized that they are advantageous in different circumstances.

Operations and Maintenance Facility

One disadvantage of operating a separate line is the fact that you need a separate OMF, to park" the trains. If you run trains through the night (like they do in New York) you may not need parking facilities for all train sets. With automated trains you may even store some along the route, for example in a tunnel segment. But you still need facilities to clean and maintain the trains. There is a property west of the BNSF railyard which may work or you could build it on the Armory site.

Labor Concerns

Both Metro and Sound Transit currently have trouble hiring enough drivers. If we expand our transit network, we will need more drivers as well as maintenance and other personnel. Not having to worry about drivers for this line may ease the burden somewhat, but operating more hours may also increase the need for other staff.

Alignment

The quickest way to build a separate line would be to use the existing preferred alignment, scale down the stations and start construction. Since it would not involve downtown tunnel construction, construction could start much sooner. With the station footprint much smaller, it might also be useful to revisit some other options such as going all-elevated or at least increasing the elevated portion of the line.

Regardless of the alignment, automated trains would allow for more frequent trains, longer operating hours, more flexibility with station placement as well as a reduction in construction costs, complexity, and associated disruption.