I just made the trip this morning. It turned out to be 20 miles, instead of 17.5 that I presumed, it only took 1.5 hours of riding.

I did get the maps from cascade bike club. It lead me to king county bike maps, which shows an un broken trail from Bellevue transit center. The actual trail, as I found, breask up into several sections of road that don't have bike lanes. (this is where my confusion came in earlier)

This time, I followed the road it cut out on for a couple miles, and I got a bike path again. woohoo. 20 miles is my longest single distance yet.

(Thank you [mimitabby] for the map suggestions. that will be helpful later for other routes.)