Fasteners believe to be left by locals who disagree with additional infrastructure
I honestly can't even imagine what kind of scumbag would take the time and effort to deliberately try to put people in harm's way by doing something like this.
I'd be stoked for more bike infrastructure in my area. Fewer methheads on their rusty deathtrap bicycles meandering across traffic. Although, the people that treat their riding lawnmowers as cars would likely use them too.