The Interurban is confusing, I think. We live very close to it in North Seattle and have tried to continue up past 200th and can't find it. We've also tried from further north and it kept stopping and starting and was highly frustrating.
Since we're in Seattle, there IS a leash law. Nobody obeys it. DH grew up here and I guess what is now the Interurban used to be a dumping grounds then was a gravel walking trail. It's paved now and there are leash signs but people take their dogs out there and throw balls for them. The dogs also run up around the backs of other peoples yards and bark at THEIR dogs so it makes me glad we don't live right on the trail.
I've been so tempted to report the unleashed dogs to somebody but I don't know who. I'd say 95% are unleashed maybe? And when people throw balls for the dogs (they use those sticks that throw the balls fairly far) the dogs can go weaving in and out of the cyclists and runners.
I spend a lot of this time on the trail running. I hate it for riding. From what I've noticed, people seem to feel this trail is their personal backyard. They drive there not to walk their dogs but to let their dogs run free. Don't even get me started on when they bag up their dog poop (I guess I should feel grateful some of them do?) and leave the bag ON the trail!!!