I am aware that this may sound outlandish at first, but I really think they should install sets of double speedbumps in this area, as well as on Chappies.
I cycle these routes regularly, and the motorbikes, taxis, busses, Porsche group, and general sports car groups use these areas as though they were race tracks, which is dangerous to all, including themselves. I know of Porsche drivers and passengers killed on these routes.
We have recently been doing a fair bit of work in the Port St Johns area in the Eastern Cape, where taxis, buses, and all ran riot, and people and livestock were regularly killed. They have installed double speed bumps every 500m down the twisty passes, even halfway around a corner. It is absolute pain, especially in terms of travel time, as your average speed drops massively. But all the taxis need to slow to walking pace to go over them, and barely get up to speed between them.
They also have similar speed bumps in areas of Kenya to slow down large, fast, long-distance buses as they descend mountain passes or pass through villages, and it works.
It is a drastic measure, but it does really slow down all the mad drivers.
