Re: Train Order working in NSW

[Eddie Oliver <eoliver@efs.mq.edu.au>]

Dave Proctor wrote:
> 
> What about FPL's, they same way they work in the metropolitan area, i.e. the
> FPL is unlocked, the points move, the FPL is relocked. When the points are
> to be restored, the FPL unlocks, the points move, the FPL relocks.

There are a few ground frames - especially those associated with
emergency crossovers - which are like that. The releasing lever is
separate from the FPL, and the FPL will lock the points both ways. 

However such an arrangement is significantly more expensive, and it
would be a big job to go around replacing all the two-lever frames with
three-lever ones.

There are some good reasons for the two-lever frame arrangement. The
very fact that the removal of the releasing key locks the FPL in its
locking position, and this can only happen if the points are normal, is
a safety feature which prevents the points being left non-normal. It is
of course possible to achieve the same result in a three-lever
arrangement, but with greater fuss.

Like so many of these issues, it is a combination of history and
economics. The nominally "safer" arrangements could be made, albeit with
some side-effects, but they would not be regarded as cost-effective.

> See above. If the FPL had to be locked (whether set for the loop or the
> main) then accidents would be less likely to happen, as two levers would
> have to be swung instead of one.

Just in the last few days there has been a fairly major accident in
Canada where points were left set (but locked) the wrong way. 

Eddie