:: My take: We should defer to how the owner/operator/builder categorizes such systems in cases like these. This is pretty similar to the Confederation Line instance – while it may be fully grade-separated, it's hard to argue when the operator self-categorizes it as "light rail". But the Seattle case is even more clearly light rail, as this is simply a fully grade-separated extension of a line that is currently fully light rail. San Diego's coming Mid-Coast Trolley extension is the same thing (fully-grade separated), but that won't suddenly make the San Diego Trolley (or even that part of it) "metro".