why was the successive double yellow/repeated AWS issue just a southern issue? surely the same was true on many busy lines north of the Thames? Surely the lines out of Liverpool St and Fenchurch Street were the same?
and was the higher power AWS magnets really so technically difficult?
Or was it really the Southern region being independant?
Then again there was Signal Repeating AWS. originally it was Southern Region AWS or SRAWS. An opportunity missed IMHO. double yellow issue solved.
Signalling-wise, all the regions were independent. Each region had its own standard way of doing things, regardless of what HQ said. Each region had its own typical circuits, its own standards, and their own interpretation of HQ standards (in many cases, the interpretation was "ignore it, carry on doing it our way"!). It was only really the introduction of Solid State Interlocking in the late 1980s that forced the regions to conform, as they had to use the same data constructs.
In the early days of AWS, the Southern took the view that rather than spending money fitting AWS to semaphore distant signals, a better safety return could be achieved for the money by converting the distants to colour-light.
The need for higher power magnets to be developed also delayed the introduction of AWS in the early days. In addition, the need to source the higher power was an on-going problem, particularly for suppressed magnets which draw a lot of power (the original green suppressors could get too hot to touch). Ironically, even in electrified areas where you might think getting a power supply should be easy, power could be a problem. Unlike in AC traction areas, where significant work usually has to be done to make the signalling immune to the traction, in DC traction areas very little immunisation work was needed. So in the DC electrified areas there were many signalboxes that still relied on the same dry-cell battery power-supplies as they had pre-electrification.
Certainly the issue of repeated double-yellows was considered a big issue by the Southern, which is why the Southern Region AWS (SRAWS, or Signal Repeating AWS as it was later called) was developed. In the inner suburban areas, particularly in the four-track areas with parallel signals on fast and slow lines, much of the signalling was designed so that the double-yellow gave braking distance for the fasts, and the single-yellow gave braking distance for the stoppers. This allowed the required headways to be achieved for both fast and stopping trains, with fairly uniformly-spaced signals in parallel on both fast and slow lines. However, it meant stoppers routinely ignored the double-yellow and only commenced braking on the yellow. I can't say why other regions didn't think this such a big issue, but I suspect (because their signalling often tended to be much "messier" in the inner suburban areas, often with different signal spacings or additional signals on the slow lines) that the signalling wasn't designed on the same basis.
