the springwater trail is under construction, so you won't be able to get past johnson creek blvd (i think)...but when it's done (i think november) it is definitely quick. if you are worried, bring mace or a knife. i always keep a knife in my bag...people are insane.
and i use the hawthorne bridge, too. even though powell is shorter from where i am, all i have to do is bike back up a few blocks once i'm over, and i think it's worth the extra 5 minutes to not have to worry about death during the bridge ride.