Hi all, I've noticed at certain stations, usually near the headwall and beyond the barriers at the end of the platform, there is a black T on a red background with a white cross through it. Does anybody know what this sign means? Thanks
As others have said it means Tunnel Telephone out of order, however, if the sign is displayed it does not necessarily indicate that the T/T is out of order!
The line controller would inform the station supervisors to display the sign if the T/T was out of order at their station. Similarly when the circuit had been repaired and recommissioned the controller would tell the station supervisor to remove the sign.
In many years as the maintainer of T/T equipment and circuitry I encountered some stations where the signs were on display all the time, some supervisors seemed to be unsure or unwilling to accept that the T/T was in commission and in service. At one particular busy station the signs were always displayed and I would have to get the controller to ring the supervisor and tell him to reverse the signs. Next visit the signs would be on display again for no good reason.
I was always aware of what was out of commission and why as I was the chief maintainer for the line and was informed of all faults on a daily basis. T/T repairs were top priority as Safety circuits and apart from exceptional circumstances were usually repaired in engineering hours on the day the fault occurred.
Some tunnels are quite damp in places and in those areas the wires will corrode over time and sometimes break in traffic hours causing collateral damage such as blowing track circuit fuses resulting in signal failure and delays to service while a lineman tidies up the site, recovers the broken wire from the track and makes it safe and then resolves the signal failure. Broken tunnel wires cannot be repaired in traffic hours without suspending service so the controller will override the affected circuit, report the fault and call the affected stations to get the 'T' boards displayed.
Other possible causes of T/T out of commission are due to being unable to reset the system following its use in an emergency. There are several ways that, that can occur and not always as a result of circuit failure! Again the controller would run service with T/T 'OOC' pending a subsequent night investigation of a 'Tunnel Telephone Operation'.
Sometimes such an investigation will uncover a 'change of T/T line characteristics' associated with damp tunnels, specifically a lowering of insulation resistance which puts the electrical parameters out of specification. A circuit may then be out of commission for several days while the T/T wire insulators are inspected and cleaned to achieve the electrical specification. This is a relatively rare occurrence but it happens. Tunnel dust, grease, water and chemicals combine very effectively in damp areas to degrade T/T circuit parameters. One unusually long section with more than 500 insulators took a week to put back into service.
Similar to the 'T' board is the 'R' board used to indicate 'train radio out of commission'.
