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GWR Route: Banbury to Wolverhampton
GWR Route: North Warwickshire Line
Birmingham Snow Hill Station: gwrbsh1742
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Electrically powered mechanisms for operating semaphore
signals were more complex when they were interlocked with route indicators.
This is a close-up of the mechanical linkages and electrical contacts on the
signal post at the south end of platform No 7. The main up platform line
Starting Signal was a standard four foot long, lower quadrant semaphore signal
at the top of this post, but it is just out of sight in this photograph. It was
controlled by lever 4 in the Birmingham South Signal Box. This lower signal was
what is termed a Draw Ahead or Shunting signal and was
distinguished by its lower position on the signal post and by having a shorter
semaphore arm (three foot long). It was provided to regulate the passage of
trains without authorising them to pass any Stop Signals which were set to
Danger, this could be used to either: a)
direct a train or locomotive into a siding b)
authorise a driver to pass the Starting Signal for shunting purposes
only c) instruct a train to be drawn forward
closer to the Stop Signal. This final instruction option was not introduced
until after 1923, but it was a regular requirement at Snow Hill, where the long
platforms were designed to
accommodate two trains - one
before and one after, the centrally positioned scissor switches.
This
semaphore signal at Snow Hill was interlocked with the route indicator above it
and when the signal was operated to clear, this would illuminate the required
instruction as follows: Engine Spur
lever 30 from Birmingham South Signal Box
Shunt lever 5 from Birmingham South Signal Box
The engine spur
was a short siding located adjacent to the up line at the tunnel entrance.
Robert Ferris
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