Every time I see these things I am impressed with the elegance of the idea.
Some clever soul thought of off-setting the vertical infill bars in the pedestrian guard railings near crossings in such a way that kids were visible through the railings before they ran out across the road.
No extra materials, and only a tiny amount of extra thought during manufacture.
Leicestershire County Council has some information about viewing angles and appications here.
Mr Google delivered UK patent number GB 2414747, which brought up the issue of see-though posts and, more importantly, led me to the clever soul: original inventor Dr Douglas Stewart
Read this facinating report by him – particularly the later bits about subtle visual errors at junctions.
The simple ideas are the best.
If you can answer this, respond below, or to alice@electronicsweekly.