Don't have anything to add about the better approach to mapping protected bike lanes, but agree that MapRoulette could be a good way to fix the duplicated representations. I would set as an "expert" task. 

Just to restate the issue as I understand it: across Cambridge/Somerville, bike lanes currently represented in both the roadway tags and as a separate way. Where mapping separate cycle ways, bike-related road tags need to be removed and the tag "cycleway=separate" needs to be added. Is that true?