Barriers that do the job

This set of barriers seems to do the job

At a cross-roads in Charing, On this side of the A20 (which passes through the village), and at the mouth of the road to Pluckley.  There are similar crash-barriers on each corner, which are actually placed to protect pedestrians ~ must have been a different engineer from their normal; fellow.    Why at one place and not at so many others?