Re: NRC <> Brisbane to Sydney safeworking.

["Michael Walker" <walker@hotkey.net.au>]

>What if the computer suffers a power out for a fraction of a second and
resets.
>it then boots up and issues an oerder for a train that is heading for the
train
>it issued an order to before it went down.
>
>and computers do make errors. what if it gets a fualty byte in it's memory
and
>that corrupts the data been carried?
>
Without knowing for sure how cheap and nasty the computer systems used for
present safeworking systems be they CTC or SAW, a lot of these errors can be
avoided. If a computer suffers a power out for a fraction of a second, I
presume the UPS installed would keep the PC running until either the power
resumes or it can be safely shut down.

When it is rebooted, I presume the database of logged track orders would
come back on line too and take note of where trains are supposed to be and
not issue conflicting orders.

As for corrupt data, I would assume that if it is on the hard drive that
whatever system is set up for mirroring the hard drive be it a redundant
drive or redundant server would use the correct data. If a redundant server
is running, that would also fix your memory (and probably your rebooting)
problem.

I think I can safely assume that a computer system is just as reliable as a
manual system from a fault tolerance point of view. Indeed, I would think a
computer safeworking system is more reliable as it won't permit ANY
incorrect moves if set up correctly, unlike a manual system. I know one
station that shunts trains without the driver always having the staff, even
though they need to go up and back part of the single line. The reason being
that when the train gets to the yard, the driver has to walk back to return
the staff. The driver can't be bothered and the station staff get annoyed
because they have to wait for the previous train on the single line to get
to the end before they can get a staff and then hold up the next down train
whilst they shunt. If the timetable is running behind, it creates all sorts
of problems, then Metrol give them a please explain. Plus it makes the
current timetable difficult to keep.

So when the driver gets to the yard, he gives a toot and the staff is sunk
by station staff (assuming it was removed at all - in this case the driver
relies on the fact that the safeworking officer won't release another staff
whilst he is on the single line). Is this a good example of the safety of a
manual safe working system?