I lived in Manor Mount for a few years and I remember what it was like when you could turn down into it from Honor Oak Road.

The problem wasn't at the top end. It just led to a traffic jam at the bottom - as I'm sure you can imagine - which tailed back round the bend and past the ambulance station (!!!).

Then of course there was the other issue of all of those extra cars having to run the gauntlet by turning left, or the occasional right, from Davids Road onto the South Circular and there were near-misses every few minutes.