Link’s vehicle shortage provides both challenges and opportunities. By deciding to batch the order for the remaining 122 cars needed to operate ST2 (Lynnwood-Overlake and Lynnwood-Angle Lake), Sound Transit chose economies of scale at the cost of limited operational flexibility in the interim years between ULink and new vehicle delivery (2016-2018). In practical terms for riders, this has meant the inability to operate all 3-car trains at weekday service levels.

Before Sound Transit selected Siemens as the vendor instead of KinkiSharyo (who built the cars you ride today), we asked that the new vehicles feature “open gangways”, nerd jargon for cars that you can walk between and through. Open gangways maximize platform space available to passengers, and are the global standard for urban rail. But in another example of negative American exceptionalism, these best practices are universally ignored here. To see open gangways in practice, Seattleites only need to visit Vancouver and ride the Canada Line.

So with this new procurement, Sound Transit has a chance to align itself with global best practice and build open cars, maximizing passenger capacity and taxpayer return on our investments in ST2 (and soon ST3). Otherwise, every 4-car train set will have 8 operator cabs forever.

In 2015, Sound Transit spokesman Bruce Gray told STB that open gangways would “limit flexibility within the fleet and the Operations and Maintenance Facility (OMF) isn’t set up to handle longer vehicles.” Asked to clarify last week, spokesman Geoff Patrick struck a similar note,

The reasons all Link trains are planned to continue featuring operator cabs at each end are not related to the incompatibility of different vehicle types with our maintenance facilities…(that would not likely be an issue for vehicles of similar length)…but rather to maintain the flexibility needed for efficient and effective train operations. To keep operational flexibility with a fleet and system of Sound Transit’s size, we need to be able to place any light rail vehicle in any position within a trainset. Twin operator cabs at either end of the vehicle give Sound Transit this flexibility. This will be especially important when all trains are operated as four-car trains and peak-hour headways are as frequent as every three minutes. Other benefits include the ability to cut trainsets from quads to doubles or any other trainset configuration that suits the operating situation. This is also important for train rescue operations. No matter if a trainset is a single, double, triple or quad, having the ability to reverse direction from the terminus station is an absolute factor in running revenue service. We have not analyzed how much additional passenger space could conceivably be added if Sound Transit were to adopt a framework that would be inconsistent with the vast majority of light rail systems in sacrificing this flexibility.

While operational flexibility is indeed important, whether or not it is paramount is a valid policy question. Let’s parse this statement a bit.

That would not likely be an issue for vehicles of similar length

Open gangways need not mean longer vehicles. It can mean standard length vehicles coupled and articulated, broken apart as needed for maintenance. Those asking for open gangways aren’t necessarily looking for a 400′ vehicle, but perhaps something like two 200′ vehicles.

We need to be able to place any light rail vehicle in any position within a trainset. Twin operator cabs at either end of the vehicle give Sound Transit this flexibility. This will be especially important when all trains are operated as four-car trains.

The flexibility suggested here is most applicable now, and least applicable in the full ST2 context; after Northgate opens in 2021, the plan is all 4-car trains all the time. It is reasonable to think that boosting capacity every day could be a more important policy goal than back-end operational convenience or resilience in the case of a breakdown. After all, in the case of a breakdown, non-revenue trains can be up to 8 cars in length per Kinkisharyo’s specifications for the current trains, so ST could send a tow car.

We have not analyzed how much additional passenger space could conceivably be added if Sound Transit were to adopt a framework…

It is relatively simple to get a rough idea of the capacity boost that would be possible. Link vehicles are 95′ long from coupler head to coupler head, and the diagram below shows the current fleet’s dimensions (in millimeters).

From this diagram the usable passenger space is roughly 24m, or 78 feet. Operator cabs and couplers take up the other 18′, or 19% of total car length. For a typical 4-car transit on a 400′ platform, proportional usage would be as follows:

From the above graphic, fully open gangways could conceivably add 54′ of platform space, a 17% boost in passenger capacity. If trains had two 200′ cars with operator cabs and couplers in the middle, we could still add 36′, or a 12% boost. Is operational convenience worth foregoing this capacity forever?

…that would be inconsistent with the vast majority of light rail systems in sacrificing this flexibility.

This appeal to precedent makes sense in the context of low quality, low capacity North American light rail systems, but not fully grade separated Metro systems. If you view Link as closer to the latter than the former, as I do, then appeal to precedent should run in the other direction, toward the open gangway global standard. Open gangways would turn 4-car trains into “4.5 car trains” for pennies compared to the cost of lengthening platforms later. When it comes to adding capacity to a nascent rail network, there will never again be lower hanging fruit.