Ah right, it presumably connected two different railways, who I guess at that time had different rules and regulations and ways of working. If it was block worked then maybe the issue was they had different bell codes and that caused confusion?
Good one.
@SteveM70 - that's exactly the primary cause.
It was the AM peak. The eastbound North London Railway was recovering after being blocked at Dalston by a locomotive with a blown boiler tube. The NLR signaller at Canonbury Junction had received 6 beats ("line obstructed - positive block") from Canonbury Station and passed this on to the GNR signalman at the GNR No 1 box just north of the tunnel. The GNR man was faced with a series of NLR suburban trains heading from the ECML to Broad Street and kept sending 1-2 beats ("be ready - is line clear for passenger train?") to Canonbury Junction. At some point, as the line towards Dalston Junction was clearing, the Canonbury Junction signaller sent 7 beats ("obstruction - permissive working") to GNR No 1 in response. This wasn't allowable on GNR territory except on goods lines, but the GNR signaller (who was a relief man who worked at different boxes) looked at the NLR bell codes card and interpreted it as allowing him to send trains forward under caution. What he should have done was contact the NLR signaller and agree on how the section was to be worked. What he actually did was to start working the section on the time interval system. He had sent four trains forward in this way without cautioning the drivers and only stopped when the guard of the second train reached his box to tell him that there had been three collisions in the tunnel, the first train having stopped at the junction protecting signal.
The GNR signaller was entirely blamed for the accident, but I can't work out why the NLR man didn't send 6 beats to the GNR box as soon as he knew the first collision occurred. Instead he appears to have kept sending 7.
So what was standardised was the system of bell codes.
Your floor.
