As an anecdotal comment, i visited The Gambia in West Africa a few years ago and was surprised to discover that one area of town is officially called "Traffic Lights". They were the first set installed in the country in 2001.
In the developed world it seems quite hard to explain the landmark concept -- people know and use maps, addresses are available everywhere, online maps are ubiquitous etc. Whereas people from developing countries seem to get the idea much more easily.
This blog post explains why we are focusing on that simple concept.
