Another constrained-choice system: Poles in the sidewalk ensure that cars don’t turn on to the (very broad) Parisian sidewalks, while permitting bicycle, motorcycle, and pedestrian traffic to pass through. A kind of semi-permeable membrane for the four-wheeled set.

The poles are also a way of claiming turf and delineating space. They are also a handy way to notify pedestrians that they should expect auto traffic.