Re: [VIC] Hypotheticals of gauge change!!

[Chris Brownbill <cbrnbill@enternet.com.au>]

Maurie Daly wrote:
> 
> The problem with this argument is that it should then also apply to check
> rails where we have another rail only a few inches away from the running rail.
> Check rails are used on all points and on most bridges ,yet there is no 80
> km/h speed limit present because of check rails.
> 
> MD
> 

Well yes, but my understanding of check-rails is that they reduce the IMPACT of
a derailment even though they slightly increase the LIKELIHOOD of one, and that
in situations where the consequence of a derailment is grave (eg on a bridge or
at points) this is a positive trade-off.

For example, at a set of points without check rails, the likelihood of a
derailment is HIGH and the impact is MODERATE to HIGH (Ararat on Friday
night???).  With check rails, the likelihood is still high, but the impact is
reduced to low.  On a bridge without check rails, the LIKELIHOOD of a derailment
is LOW, but the IMPACT is HIGH.  With check rails the likelihood is MODERATE and
the impact is reduced to MODERATE.  The likelihood can be minimised by
minimising the length of check-rails to absolutely no more than the length of
the bridge or the few metres following the point frogs and blades.

On plain track however, the likelihood of a derailment is LOW and the impact is
LOW.  On dual-gauge track, the likelihood is raised to MODERATE and the impact
is still LOW.  Unfortunately for this scenario, the increase in likelihood is
proportional to the length of the track which is usually much longer than the
length of check-rail at points or over bridges.

Hence my understanding of why check-rails are considered, on balance, to be a
positive risk management strategy for short sections of high derailment risk
track, but not on long sections of low derailment risk track.

Of course I'm not an engineer so this could all be intellectual bovine excreta.