Obscure oddities

And the rail gap - what little there is of it - is visible as a break in the conductor rails. The route of the cables feeding the next section can be seen in front of the PW trolley.
Let me explain the problem with that gap and, to make it more interesting, let me use the rules and regulations that would have applied at that time – the late 1940s. Although much of this still applies today, I will speak about it in the past tense to ensure that everything is in context.
Let us imagine that a train stopped in the tunnel and the motorman discharged the traction current by rubbing together the tunnel telephone wires. He (no women motormen or guards in those days) would have clipped-on the tunnel telephone and tried to speak to the sub-station attendant to explain why he had taken this action. If no contact was made, the sub-station attendant would have assumed that the current had been discharged as the result of a fault and he would have restored it after a few minutes. Even if contact had been made, the train crew would have placed short circuiting devices (SCDs) across the track at either end of the train to prevent current being restored. It was also generally understood that current would never be considered to have been discharged until SCDs were in place – the act of discharging current by using the tunnel telephone lines was not considered to be reliable. The SCDs also served another purpose that is directly related to the photograph that we are discussing.
If there was a short rail gap (as in the photograph) there was a danger that the carriage of another train could bridge the gap, allowing current to pass up one set of collector shoes, down the other and thus liven up the ‘dead’ section of track. This is one reason why SCDs were required to be placed even if current was off: And because this could happen from both ends of a section, the SCDs were placed at either end of the train and left there as long as the crew required protection from the traction current. The other reason that SCDs were placed at front and rear of a train was to ensure that, if a train sat in two sections, both sections would be discharged.
The question remains, how would a carriage get into a position to bridge the gap? Well, the regulations stated that if a motorman became aware that current had been discharged he should consider it to be an emergency and he should bring the train to a stop as soon as possible. If a train was crossing such a short gap when the current went off, each car crossing the gap could liven-up the dead section of track by passing current into it from the live section. If the signal went to danger, it would trip a train that was passing and could cause it to stop with a carriage across the gap. There was also the possibility that the stranded train could be bridging the gap itself until the current was discharged in both sections!
One way around this was to make the rail gaps longer than the distance that could be bridged by any two collector shoes within a single circuit. That is why you see long rail gaps.