There is indeed a route:
http://www.gmap-pedometer.com/?r=1473835
My husband rides it (at least in the nicer weather). He says most of the major road crossings have lights, or are otherwise not difficult. He's going all the way to Tualatin; I just showed the part to Tigard.
The fuzzy mapping part is the Fanno Creek Trail - doesn't show as a road on gmaps.