Most drivers and guards now seem to have mobile phones, while not a
secure comms medium, mobile phones are probably better that the traffic
radios.
All stations and signals boxes should have emergency mobile phones, the
3 watt 'bag' types, that can be hooked to a car battery. A signal box
might need two such phones.
The phones need to be left disconnected from power and the lead-acid
car batterys kept charged by a filtered charger. (ie we dont want the
backup phones fried if lightening strikes the radio tower on the signal
box)
When lightening fries the signal box, blowing the interlocking and
comms system, one mobile phone could be used to restablish contact with
control, the other number, 'published' in circulars, could be used by
drivers and guards to get further information. The piddly little 450.050
traffic radio's could be used by station assistants ( or any other
qualified person they could lay their hands on) to manually operate the
yard. Things would be slow, but not a total log jamb.
Unfortutnatly even with this, at some point traffic will have to be
halted for 15-20 minutes or even longer so the signal electricians can
do a functional test of the interlocking without things changing state
under them.
-- Matthew Geier, matthew@law.usyd.edu.au Computer Systems Manager, +61 2 9351 0240 Law School, University of Sydney +61 2 9351 0200 (fax)