AWS in absolute block

[autotank]

Why is only the distant signal fitted with AWS? Is this only the case with semaphore signalling or is it also the case where AB in use with colour lights?

Also are there many semaphore distant signals left on the network (that aren't fixed).

Thanks in advance!

 

[driver9000]

I asked this when I was a trainee. The reason I was given was that only Distants have AWS is because should the horn sound with the Distant on, the Home signal may be off and recieving an all clear bell could cause the Driver to think all stop signals relating to the Distant are off. The routes I work over have a mixture of semaphore and colour lights. Only the IB colour lights signals have full AWS indications. The semaphore Home/Section signals do not if that makes sense.

There are 4 worked semaphore Distants on my routes (ie ones that show both indications).

 

[autotank]

Thanks!

I would assume the section signal would have TPWS fitted (but not AWS). What about TPWS on Home signals?

 

[driver9000]

That depends on the signal, not all signals are TPWS fitted. Some of the semaphore signals I work under are, some aren't. The IB colour lights aren't TPWS fitted.

 

[Zoe]

Also are there many semaphore distant signals left on the network (that aren't fixed).

Droitwich Spa's Up Main Distant is one.

 

[TDK]

Thanks!

I would assume the section signal would have TPWS fitted (but not AWS). What about TPWS on Home signals?

TPWS will only be installed if when the risk assessment is carried out that the train cannot stop before the overlap or the risk is high for a collision, most automatic signals are not fitted with TPWS. There are a lot of semaphore and colour light signals in AB fitted with TPWS as the risk is high if a SPAD occurs.

 

[455/8]

The section between Aldershot and Farnham on the Waterloo to Alton line is absolute block with colour light signals and all the signals are fitted with AWS.

 

[OuterDistant]

I always assumed it was a cost-saving measure that allowed the "safest" way of only equipping one signal.

If AWS was installed at the home signal only, an inattentive driver would potentially receive a warning only seconds before crashing into a train waiting at the starting signal.

 

[TDK]

The section between Aldershot and Farnham on the Waterloo to Alton line is absolute block with colour light signals and all the signals are fitted with AWS.

There are quite a few areas like the - Stockport is one of them. If the signals are all replaced with colour light then usually AWS is fitted.

 

[John Webb]

The original AWS as applied to semaphore signals was the ramp system introduced by the GWR. Their original idea was to actually do away with distant signals and the associated costs of maintaining them, particularly the long wire run most of them needed for operation. It would also eliminate the need for 'Fogmen' to be sent out to remote distant signals in foggy weather.
The set-up was that if the driver ignored the warning, the brakes would be applied to stop him before he reached the first stop signal to which the distant applied.
This is a bit different to the present system with colour light signals where any signal can, in effect, be the distant to the next signal and so every signal is fitted with AWS or the modern equivilent.

 

[Old Timer]

Why is only the distant signal fitted with AWS? Is this only the case with semaphore signalling or is it also the case where AB in use with colour lights?

Also are there many semaphore distant signals left on the network (that aren't fixed).

Thanks in advance!

The answer to this lies in the history of AWS.

AWS was the development of the system used by the LTS (part of the Midland Railway) out of Fenchurch St.

THe purpose of AWS was to give a warning to the Driver of the position of the mechanical distant signal during poor weather conditions so that the driver could bring the train to a stand at the Home signal.

AWS was never designed to be positioned at other than distant signals. With the advent of MAS, signalling principles set out that AWS would be located at every signal capable of displaying a yellow or double yellow aspect.

Of course as pretty much all MAS signals could display those aspects then it became the norm for AWS to be installed at every signal.

 

[455driver]

Adding to OTs post,
AWS will only tell you if a signal is green or not (the reasons go back to its introduction), it doesnt diferentiate between red, single yellow or double yellow.

I spend a lot of time cancelling AWS horns.

 

[Old Timer]

455 Driver
Thank you for that.

I should have included that bit of information as well for clarity, so thank you for adding that in.

 

[455driver]

No problem OT, glad to add a little.

 

[dk1]

Most East Anglian branch lines didnt even have AWS on distant signals until the late 90s. Thig fog was a nightmare to drive in before then with the knock on performance issues.