I've seen municipalities put up bendable bollards to create a more defined bike lane. I've also seen concrete barriers used on highways to create a 'narrow lane zone' accommodating construction.

The bollards and barriers were placed in the same fashion, directly on the outer line of the lane. Despite this placement not actually narrowing the lanes, in both cases it does slow traffic to below the posted speed.

Not being able to drive over paint as you please along with there being real and immediate consequences for straying from the lane is enough to slow people down. Having cameras issuing speed fines is a bandage solution.

The best case scenario is that they are installed as temporary measures to raise funds to redesign infrastructure to eliminate speeding as a common problem, then the cameras become obsolete and are removed. I've not heard of this ever happening though. Oh to dream.