This is what I posted about it:
On the off-ramp from the N3, northbound, for both the London Road exit for Alexandra (a township) and the next exit (Marlboro Road) for Sandton, the richest neighborhood in the northern suburbs of Johannesburg.
Even the Automobile Association map of Johannesburg has a note next to the exit for Alexandra warning drivers not to use this exit except for access to Alexandra. Apparently enough rich people took the exit (which is in fact a more direct route to Sandton) and got carjacked by armed poor people.
Alexandra is a township where the government is trying hard to turn the shacks into tract housing. You can see from the motorway that they really have built many, many little houses, complete with electricity.
http://r-ness.livejournal.com/24862.html is my original post.