I use Wandrer.  It is a a subscription website that challenges bikers and walkers to ride or walk every road.  The problem with marking the Ross Island bridge as "bikeable" is that there are then several thousand users that are going to really want to try and complete those.  I stood with my bike on an early Sunday morning for a long time and given the volume and speed of traffic and lack of any shoulder and narrow lanes, marking any of that as bikeable or walkable is flat out dangerous and irresponsible when the sidewalk is already a designated crossing path.  But, no, I don't have "proof" that it is illegal.  All I know is that of all roads in Portland (and I have now ridden 93%), the Ross Island is the only one that functions like a freeway (high, fast traffic)...the whole point of not allowing bikes on our city freeways.