What frustrates me most where I live is poorly marked bike lanes/paths. My neighborhood is surround by 'multi-use paths' that consist of a wide finely crushed gravel path next to a double wide sidewalk-like path. These are supposed to be used by cyclists as well as horses and pedestrians, and when used as such are glorious and completely safe.

Problem is, many cyclists don't realize they are for their use, and wind up riding on the narrow, winding, traffic-calmed streets where it's most definitely not safe or convenient for cyclists or motorists.