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Do, or could, MCB-OD crossings check for the line being clear before raising their barriers?

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IanXC

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In the context of this incident and others of a similar nature:


RAIB said:
At around 05:50 hrs on 11 January 2018, a car collided with the rear-most wagon of a stationary freight train at Stainforth Road Automatic Half-Barrier level crossing, near Doncaster. The crossing’s warning equipment was not operating and its half- barriers were raised when the car approached and entered the crossing.

In essence there can be an issue with AHB (Automatic Half Barrier) crossings where the barriers are raised after a preset amount of time, the risk being that a train is still across the crossing.

My question is, given the MCB-OD (Manually Controlled Barriers - Obstacle Detection) crossings check for the presence of obstructions on the carriageway before lowering, do, or indeed could, they check for the presence of obstructions on the carriageway before raising? The net result would be that the circumstances in the above report could not occur at an MCB-OD crossing.

Wonder if anyone knows the answer to this?
 
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Bald Rick

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In the context of this incident and others of a similar nature:




In essence there can be an issue with AHB (Automatic Half Barrier) crossings where the barriers are raised after a preset amount of time, the risk being that a train is still across the crossing.

My question is, given the MCB-OD (Manually Controlled Barriers - Obstacle Detection) crossings check for the presence of obstructions on the carriageway before lowering, do, or indeed could, they check for the presence of obstructions on the carriageway before raising? The net result would be that the circumstances in the above report could not occur at an MCB-OD crossing.

Wonder if anyone knows the answer to this?

I don’t know for certain, but reasonably sure the obstacle detectors do not scan for a rail borne obstruction before lifting. No reason why the logic couldn’t be altered to permit it, although it would extend the down time slightly.

However, I’m fairly sure that this sort of incident couldn’t happen at an MCB OD as the crossing would fail down in the event of a train being could of it for an extended period, and the barriers only raised by a technician on site.
 

IanXC

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However, I’m fairly sure that this sort of incident couldn’t happen at an MCB OD as the crossing would fail down in the event of a train being could of it for an extended period, and the barriers only raised by a technician on site.

I thought the trigger logic for an MCB-OD sequence was the same as for an AHB, as per the increasing number of conversions?
 

TSG

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In essence there can be an issue with AHB (Automatic Half Barrier) crossings where the barriers are raised after a preset amount of time, the risk being that a train is still across the crossing.
Not where they've been designed to more recent standards, as referenced in section 39-44 of that report.
I thought the trigger logic for an MCB-OD sequence was the same as for an AHB, as per the increasing number of conversions?
No. It's essentially the same as a MCB CCTV but with ODs instead of cameras and automatic operation. An MCB-OD is interlocked with the signals whereas, broadly speaking, an AHB isn't.
I don’t know for certain, but reasonably sure the obstacle detectors do not scan for a rail borne obstruction before lifting. No reason why the logic couldn’t be altered to permit it, although it would extend the down time slightly.
There's no requirement for it in the standard and the extended down time is reason enough not to. It's unnecessary because the arrangement at Stainforth Road, where the crossing is only held by a track circuit on the approach to the crossing, is no longer permitted AIUI. You must prove the train clear of the crossing to raise it.
 

IanXC

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Interesting stuff, thanks. I hadn't realised the Stainforth Road situation was no longer permitted. I guess linking to existing track circuits and/or adding them was the chosen option rather than relying on the OD was the chosen solution.
 

TSG

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Track circuits/treadles and axle counters have demonstrated reliable operation for decades. If you're going to the trouble of changing an AHB to an MCB-OD, moving some track circuit/axle counter section boundaries is a minor part of that work, especially as most (if not all) of the alterations will probably be at the crossing where everything is being renewed anyway. There's no compelling reason to use a relatively novel system like OD instead. Not until ETCS Level 3 anyway :)
 
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