AWS

[Archie]

Anyone got any lit on all the different types of AWS?

Many thanks

[PJW]

Anyone got any lit on all the different types of AWS?

Many thanks

Not really sure what you are after.......

Functionally there are two strengths of AWS; the usual Yellow and the extra-strength Green for use on dc electrified lines.

There are three types of each: the plain permanent, the suppressed permanent and the electro; obviously also a whole host of mounting paraphernalia etc. that is of practically no interest from IRSE Exam viewpoint but very significant for a proper site installation.

Over the years there have been various variants of each type,made possible by technology advances; first the yellow electros could be made to sit above the sleepers rather than requiring a ballast bed to be dug out for them, now also the suppressors.

So could you be more precise regarding what sort of information you are seeking

[Archie]

basically just want the functional information for each one, what, where and when type information etc, if that makes sense.

many thanks

[PJW]

basically just want the functional information for each one, what, where and when type information etc, if that makes sense.

many thanks

See GK/RT8035 obtainable from www.rgsonline for details.

However in simplistic terms:

a) AWS is for the caution aspect, so is provided for distant signals in mechanical signalling.

b) Nowadays for MAS signalling almost all main signals whether or not they display Yellow are fitted witth AWS- it is really just those that can't be approached such as from sidings and terminal platforms which are not provided

c) a permanent immediately followed by an electro are provided nominally 180m prior to the signal. Just occasionally there is a signal that cannot display Green (e.g. approaching a terminus) so no electro provided. On a bi-directional line the permamnent would not be provided but a suppressed permanant would be provided instead (so trains using the line in the other direction are not given false AWS indications.

d) occasionally there is a need for a suppressor in other scenarios as well; however these are very rare.

e) conversely sometimes there are opposite direction signals for which the one AWs site can be used. Hence no suppressor is needed and instead an EPE arrangement provided, the permanent being shared between the two signal's fitments and is placed between the relavant electros.

f) At highest speeds, the AWS should nowadays be provided at more than 180m; however very little of the country follows that standard. Coversely the old practice of placing AWS at lesser distances (tyically 90m) where linespeed was low has been discontinued. Alleedly drivers have been mislead as got used to AWS always being 180m before signals and used AWS as a marker and this said to be a contributory factor for some SPADs. The fact that there has been no retrospective action to move these AWS suggests that I am not the only person who is sceptical. The East London Line project recently instaled by LU to NR principles actually decided to fit AWS at less than 180m- for the very reasons why BR always used to- even though non-compliant to modern stated practice.

That's a summary- there are exceptions and more specific detail in the various relevant standards, but on the 80:20 rule the above should suffice