Seattle has had one streetcar line for some time and is just finishing up a second. What's unclear to me is why. They still suffer from the same problems that the article says led to the fall of streetcars last century: gridlock due to cars makes schedules and ride times unpredictable, same as buses. The Seattle streetcars do carry a few more people than a bus, but it's not a huge difference. From my own observations, the streetcar tracks also present a fairly significant danger to inexperienced cyclists.

We do have an expanding light rail system, which makes a lot more sense as it operates on its own right of way and thus isn't affected by Seattle's terrible car traffic.