Barbur/99W/Pac. Hwy is bikable from downtown all the way to Hall Blvd and further...but it is a little scetchy in spots. I'd highly recommend riding it at least once or twice on a weekend to learn the route and quirks in the road before adding heavy traffic into the mix.

I've also found the turns and climbs of the northern-most part of Terwilliger (around OHSU) much more enjoyable than the same stretch of Barbur Blvd. But either way you start out, you'll be on 99W for much of the route.