Crossed Whip Snake (Psammophis crucifer)
This is a fairly common snake in Johannesburg found in the hills. It is very fast and if disturbed, it dashes off for cover.
They seem to be less inclined to bite than other Whip Snakes, the ones that I have caught, I've simply dived after them into the bush when I have seen them and grabbed them with my hands. They wined themselves around grass and branches to prevent being picked up.
They are smallish, not reaching a meter in length