As long as you were, indeed, cited under ORS 811.260 (11), I agree with your logic. I can see from the street view in Google Maps, where you'd think the sign would apply to the "middle" lane and NOT to the right hand lane. The only problem I see is the "stop line" in the right hand lane, but I think your argument should still fly. If you were NOT cited under 811.260, please tell us what law you were cited under.
Be sure you print out copies of the pertinent laws and MUTCD chapters and take them with you.
Barry

