automatic signal

[khlai]

Could any one advise me?
When we say the signal is normal , it means that the signal is at red. Normally it appies to a controlled signal.
How about the automatic signal, does it become red after a train passed. Then it will automatically be clear for next train, it becomes green/double yellow. If so, how long it takes to change from red to green/double yellow.

[PJW]

Could any one advise me?
When we say the signal is normal , it means that the signal is at red. Normally it appies to a controlled signal.
How about the automatic signal, does it become red after a train passed. Then it will automatically be clear for next train, it becomes green/double yellow. If so, how long it takes to change from red to green/double yellow.

Two somewhat different subjets here!


1. A route is said to be normal when
a) the signaller has cancelled it to force the signal to be at red, AND
b) the signal trackside has actually responded and is displaying danger (not actually proved alight, but certainly not showing a proceed aspect), AND
c) can be treated as actually being able to stop a train (i.e. it has not only just been placed to red but has been at red long enough, compared to the position of any approaching train, for it to be reasonable to expect the train to stop at it)

Therefore it does apply to a controlled signal.

2. An auto signal usually shows as least restrictive aspect as it can, given aspect of signal ahead and any track xection occupancy. The time for which it is at red depends on how long it takes the previous train to travel the length that means that the section from that auto signal to clear the overlap (generally 180m) beyond the following signal. If that signal is itself an auto then that one will clear to yello once the train has travelled a similar length, thus permitting the initial signal to step up to a Green (or in the case of a 4 aspect sequence, to Double Yellow).

The time for any signal therefore depends upon train speed. Non-stop headway calculations assume trains all travelling at constant "headway" speed; stopping headways take into account the braking and acceleration if a station stop or a length of line with lower permissible speed is entailed.

[Jerry1237]

khlai,

I would disagree that the term 'normal' for any signal means red. Normal means whatever is designed to be normal. For long sections of autos, normal tends to be green as designated by a double line through the aspect rather than a single on the scheme/signalling plans. Don't forget though that the last auto in rear of a controlled signal will probably have a least restrictive aspect of green but its normal aspect should only be a single yellow. Think about why.

Similarly, in points tends to lie so the fastest route is 'normal'. However, for trapping 'normal' is the lie to derail trains!

Jerry

[Peter]

I think there are some anomalies here too. I must admit, I have not often heard the term of a signal being normal (as opposed to a route or points).

PJW, you say about a route being normal when the signaller has cancelled the route and the signal is at red and proved at red, but in pure terms, would you not expect all approach locking and route holding to have timed out (you certainly would not set route A which required route B normal until this is so).

I guess historically it all comes from the position of the lever controlling that signal. If the lever is normal then it would directly relate to an "aspect".

[PJW]

PJW, you say about a route being normal when the signaller has cancelled the route and the signal is at red and proved at red, but in pure terms, would you not expect all approach locking and route holding to have timed out (you certainly would not set route A which required route B normal until this is so).

I guess historically it all comes from the position of the lever controlling that signal. If the lever is normal then it would directly relate to an "aspect".

Indeed- that is why I listed a) AND b) AND c), with c being the Approach Locking of which you speak. [I note that I missed writing explicitly the second word AND and have now added intoo that post]

In terms of a mechanical signal operted by a lever frame, if the locking of signals against points is entirely mechanical, then the lever (to current although not historic standards) would be fitted with a "back lock" to prevent it being placed completely NORMAL in the frame- it will be able to be returned sufficiently that the signal arm is horizontal (and thus the signal displaying danger) but until it has been established that the signal has been back at danger long enough then the electric lock won't energise- the signal lever will be sufficiently "out" that the points will still be locked by it. This I think is the origin of "route normal"; a colour light signal replacing a bracket semaphore signal would retain a separate lever for each of the various routes, that used to drive individual arms / indicators on the signal post.

Route Normal does not include the asociated route locking; part of the route locking may still be locked by an occupied track in the route, but yes the route is unset and the approach locking is free.