Forum has been very quiet this year, but actually I have had a lot of attempts from a range of individuals, particularly recently; everyone seems very shy in sharing their work......
However I have permission to put some attempts on which I have commented on the Forum, so here is one of them attached with some comments written on and others below.
2012 Q9:
Again this was good; I very much liked the presentation style.
A few things that space on paper did not allow me to write:
However I have permission to put some attempts on which I have commented on the Forum, so here is one of them attached with some comments written on and others below.
2012 Q9:
Again this was good; I very much liked the presentation style.
A few things that space on paper did not allow me to write:
- You should when asked for a HAZARD always try to write it in the form
“IF <inappropriate / unfortunate / careless action>
WHEN <particular circumstances exist>
THEN <specific accident> might occur.
Your answer did infer this quite often, but could have been worded better. Remember that a HAZARD is “an accident waiting to happen” and an ACCIDENT always involves a loss (of life, of health, or equipment, of money, of environment, of reputation)
- Note that for signals it is generally the READABILITY rather than VISIBILITY which is important. Driver might be able to see a signal in the distance but may well have to be closer to know if it really is at single or double yellow, whether that is the PLJI position 1 or position position 6, whether the one he can see is for the Fast line rather than the Slow line etc.
Also that MAR is not controlling the speed of train to match the turnout (it WAS this perhaps 40 years ago, but nowadays it is about making sure don’t mislead the driver by them thinking they are routed differently than actually are- hence the important thing is that they are braking at th previous signal and the junction signal does not clear before, in totality, it is readable (unless has had a Flashing Yellow or Splitting Distant on the approach)
- Swinging overlaps are provided to give layout flexibility, broadly to allow the signaller the choice of which of several potential conflicting movements they want to make at the time when bringing a train to a red signal and have the option of then changing the allocation once a movement has been made to then swing overlap to alternative position to be able to free up another bit of the layout for another movement. You are entirely right that when the train is close to exit signal and therefore there is a chance of a SPAD that we would need to prevent such swinging for a while by imposition of Time of Operation locking, this is in case points were moving just at the time the train did SPAD and therefore may be encountered mid-stroke. Generally facing points are not called when route is set, it is the trailing points beyond it which are called- but iif they are locked or there is an opposing overlap which conflicts, then it is the facers which are called to select the other overlap.
- For the last part I think worth saying that inclusion of any extra controls can only hamper system availability- the more there is the more that can fail. Obviously if derailment at trap points, this is not itself risk free; there will certainly be delays and loss of availability of layout and if that is at entrance to a train depot the entire train service may be affected if the trains cannot get out onto the running line. Most of the other controls do also have a downside (hopefuly small compared with their advantages, but still negatives. A very slight overrun at traps will break the TCI and could therefore cause disruption for hours until rectified; during that time the line would either be closed or hand signalled and there are other risks that result from either (overcrowding , more people on busses etc; or accident following hand signalling error).
PJW