14-09-2008, 09:40 AM
alexgoei Wrote:Hello Peter,
I have reviewed your comments for the 2002 paper and have some further questions which I have entered the text in red in the appended file.
This is in particular to Comprehensive Approach Locking.
Please ignore the ones highlighted in yellow which are for me to pay attention to.
Comprehensive Approach Locking does not apply to an MAR = (Approach Released from Red) route; there would be no value. Either a) the signal is at danger since there is no train on the berth track(s) in which case approach locking would not yet have been applied, or
b) the signal is Approach Locked yet any lookback bound to fail- no sense in undertaking the task of go-looking for a train when by definition we already knoww that there is one!
Approach Release from YELLOW (either MAY-YY or MAY-FA) is DIFFERENT. The signal is allowed to clear to yellow (plus route indicator but this goes wiithout saying) before a train is on the approach. The approach release just applies to the "better aspects"; the signal cannot show a double yellow or green (or in unusual circumstances of consequtive junctions a flashing aspect) until the train is closely approaching. Hence Comprehensive A/L DOES APPLY since the signal will become locked once it clears to yellow; if the signaller replaces it to red then we need to fin out whether there was a train that could have seen it.