28-09-2011, 10:27 PM
Yes that is a good point which hadn't occurred to me; a slow moving freight would not need to call for the CCTV level crossing to be lowered anything like as soon as an express. A bit like a level crossing predictor for AHBC; there would not be a "strike-in" point as such.
The train on-board would be analysing where it would need to start braking to stop prior to the crossing, adding an allowance for the time between asking for the barriers to lower and obtaining its extension of MA (sum of system response times including the somewhat unpredictable human giving crossing clear- unless replaced by radar detection) and then calculating back at its approach speed the place at which it would need to make that request in order to get its MA extension in time.
That must be worth the 2 marks!
The train on-board would be analysing where it would need to start braking to stop prior to the crossing, adding an allowance for the time between asking for the barriers to lower and obtaining its extension of MA (sum of system response times including the somewhat unpredictable human giving crossing clear- unless replaced by radar detection) and then calculating back at its approach speed the place at which it would need to make that request in order to get its MA extension in time.
That must be worth the 2 marks!
(28-09-2011, 08:10 AM)Jerry1237 Wrote: It would also depend if it was continuous ICS or intermittent. If it were intermittent, there would be little, if any change, to the strike in distance bearing PJW's point about letency in mind (processors always take longer than relays!). With continuous, you could potentially argue a variable strike-in based upon the trains' braking performance which would decrease the strike in time which obbviously has an impact on distance. A presumption is that strike-in could be as little as braking distance plus a safety margin at line speed. That should obviously not increase the BD as it [the strike in] should already be at braking distance plus margin of the worst performing train!
There is an arguement that train bourne signalling with geographic data plus redundant balises are not quite as laggy as CBIs of old but I have no figures to support that assertion.
Jerry
PJW