Why, they in fact do. Rode on it last summer. I haven't ridden on a lot of LR systems, but this one seemed to be fairly extensive, i.e. you could get around the city fairly well and it was extensively used by the population.
Portland also has one of the deepest light rail tunnels in the nation, below a very busy public Zoo. But, I submit that local attacks are extremely unlikely, imo. People here may hate America, and they certainly despise Capitalism, but they love their city.
Atos