This is a great route, that has everything! Scenic riverside running, downtown waterfront esplanades and a really cool long stretch through the nw industrial section. You can start anywhere, but I like to start at Willamette Park, about .75 miles north of the Sellwood Bridge. From there I run north on the trail about 2 miles to the Ross Island Bridge. From there its another mile to the west side of the Hawthorne Bridge: there are waterfountains in this area! I cross over the Hawthorne Bridge on a nice pedestrian walkway, and get on to the eastside river esplanade. From there it is another mile to the Steel Bridge (watch for the water fountain about .25 miles south of the bridge). The trail recrosses the river on the Steel Bridge and one can loop back to Willamette Park for about a 9.5-10 mile run. Usually, however, I feel rarin' to go at this point and continue north on Front Avenue which amazingly has an unbroken sidewalk for 5 more miles! No stoplights to worry about and flat as a dime. I can go all the way out to a 10 mile turnaround for a 20 mile loop possibility (I have only done 18 so far) You can make the route even longer if you return eastside and cross over at the Sellwood bridge and back north to Willamette Park: that adds another 1.5 miles. Marathon training right in the heart of the big city! I highly recommend this route: it is scenic, flat, and varied enough never to get boring (and I run this route a minimum of 3 times a week!) Try it! You're likely to see me!
PS: take water w/you if you run much north past the Steel Bridge: its dry as a bone!