Re: Simple Question.....

[keithn@globalnet.co.uk]

>>. Dual aspect signalling exists due to traffic density. 

This statement, which seems to have originated with Matthew Geier is
not really correct. The traffic density can be handled by many forms
of signalling, with single or dual heads, or more and with 2, 3, 4 or
more aspects. The NSW system uses 2 heads but has little or no extra
information than the British style 3 or 4 aspect signalling using
single heads. It appears to have originated in a local and unique
adaptation of the US style signals (AAR standard) which were used with
little or no change in SA.
>
>Does anybody know how London Underground manages to runs its quite
>impressive density on what appears to be single aspect signalling? (Or am I
>wrong)

The LUL system is normally described as 2-aspect, Red for stop and
Green for Go.  It works for them because the trains have good brakes
and speeds are fairly low and uniform, wherever the red cannot be seen
from braking distance a repeater is provided.
Resignalling now is with automatic systems and is rather a different
story.
>
>Regards,
>
>Mike Alexander
>(malex@bigfoot.com)

Make friends in the hobby.
<http://www.users.globalnet.co.uk/~keithn>