Light rail is almost always some sort of bespoke system.

The only light rail operating in Washington State is LINK Light Rail, which Sound Transit operates using Siemens Mobility’s S700 model (although some older train sets are still used on the same tracks).

Looking at the Wikipedia page for the S700, you can find these trains all over the US, including California, Arizona, Georgia, North Carolina, Minnesota, Oregon, Texas, and Virginia. They seem to be popular in Europe, too. [0] https://en.m.wikipedia.org/wiki/Siemens_S700_and_S70

From what I can tell, these train sets are as off-the-shelf as can be reasonably expected, although apparently LINK has ordered their trains to run on 1500 volts as that’s what their catenaries use. Perhaps you’re thinking of BART?

-An occasional S700 passenger

No, I am thinking the Sound Transit light rail. I wouldn't be surprised if they canceled the "design for the PNW" cars and bought off the shelf ones.

Before it was built is when they said they would be custom cars.

Sound Transit operates LINK (what gp was talking about) and Sounder (not light rail, operates on BNSF tracks, coaches are made by Bombardier and seem to be in use by many commuter rail systems). Not sure what you're referring to.

The train that runs from downtown to Seatac.

That's LINK light rail, operated by Sound Transit. Here's an article about the (new) cars they use: https://www.soundtransit.org/blog/platform/new-link-light-ra... -- I get the impression all light rail cars in general are made to order per specifications, rather than off-the-shelf.

All light rail cars are custom in the same way that every airplane is custom but we wouldn’t say that a 737 is expensive because of the seat and entertainment choices.

Yah it's BART that uses an odd track gauge. Although I did read a report saying they did it to make the trains both lighter and also able to withstand wind shear in certain parts of the system.

To be honest though, I didn't find that report very compelling and they didn't back it up with actual load calculations. You really don't hear standard trains being blown over and the Bay Area isn't exactly famous for "high winds" anyway

  Yah it's BART that uses an odd track gauge

Mainline BART. e-BART uses standard gauge diesel trains and the half billion dollar Oakland Airport shuttle is a completely bespoke cable car monstrosity.

  withstand wind shear

Specifically on the Golden Gate Bridge. Which may or may not be true. The track gauge is perhaps the most standard thing about BART cars.

> Specifically on the Golden Gate Bridge

BART never operated on the Golden Gate Bridge (or any of the other Bay Area bridges).