Speaking as somebody who drives this route quite often. The speed bumps do nothing coming down the hill to slow drivers down and the hill is high enough that unless you actively brake you will pick up speed.

I agree it is not a good spot either for drivers or pedestrians. Some additional traffic calming measures need to be in place, on herne hill, on the approach to sainsburys, an electronic speed warning sign echos back your speed with a smiley face: happy, sad. I do always notice this and expect other do to, helps immensely.