In message , at 21:49:22 on Fri, 28
Sep 2012, Clive D. W. Feather remarked:
The original CSLR between King William Street and Kennington was always
Right Hand Running - no idea why.

I've read that it meant that trains arriving at KWS had the less steep
tunnel (because of the curves approaching the station). I have no idea
if that's accurate or not.

The problem at the KWS end seems to have been Swan Lane, which is just
north of the river. The tunnels were arranged vertically there (with the
northbound tunnel above), but then spread out horizontally under the
curve of Arthur St West so that both lines entered the station (one
platform) at the same level.

Under King William Street it was left-hand running, and with the
northbound line of the outside of the curve that would give it a
slightly greater distance to climb to the station. The fall on the
southbound line must have been considerable.

The tunnels then returned to side-by-side for most of the underwater
section (and beyond) this time right-hand running. At that time there
wasn't a station at London Bridge, the first one being Borough.

For whatever reason, the lines then crossed over, beneath the junction
with Borough Road, with the southbound line going under, and retained
the left-hand running all the way to Stockwell.
--
Roland Perry