Flag a specific Hazard by location rather than an entire Segment
The current system of flagging a segment as hazardous doesn't prevent another user from creating an identical or similar segment through the same hazard. This results in a large number of segments that are endlessly flagged, then recreated, then flagged again, which clog up your activity report with junk segments.
It might work better if users marked the actual hazard, such as a junction or traffic lights. Then implement a feature where you can't create a segment that traverses a marked hazard.