SHJ Interlocking

[Jim Holland]

Greetings!

	A *Traction Heritage* Xerox (don't know the issue, but it is page 
31!!!!!!!) talks about the interlocking at SHJ.  I quote:

	"About 1908 a mechanical interlocking plant and tower were 
installed, with manual operation for 24 hours a day of two derails and 
four track switches.  Cars were occasionally derailed as a result of 
confusion and switches or derails were frequently kept closed to 
accommodate certain routes for such long periods that other routes were 
penalized."
	"Automatic Interlocking Improves Service:  Replacement of manual 
track control on Pittsburgh Railways improves performance and results in 
a large annual saving in operation and maintenance."

	Apparently, this is just a partial copy of the original article 
from *Transit Journal's* Maintenance Notebook column; the date is not 
given for the conversion.
	The cover of the 1994 PTM calendar looks at two cars at the 
tunnel portal with a shanty tower in the triangle formed by the wye; no 
signal mast is evident for southbound cars exiting the tunnel.  This 
photo dates from the early 1940s

	1)--	Apparently the automatic interlocking was very late in 
the game, sometime in the 1940s; does anyone know a more precise date?

	The diagram shows a dual 3-light head side by side on a single 
mast for southbound cars exiting the tunnel with the signal head closest 
to the track being #1 and the other one #2.

	2)--	Which signal head showed track switch setting?
	3)--	Why would a 3-color signal head be needed for block 
occupancy at this location, or was the other signal head for some other 
function?
	4)--	What were the different aspects displayed by the two 
signal heads for each direction and what did they mean?

	A 3-light signal head is used for the two derails with the one 
for the 44/48 inbound cars being #3 and the one for the valley lines 
being #5.

	5)--	If an inbound interurban passes through the contactor on 
signal #5 to set the derail for entering the tunnel  AND  an outbound 44 
or 48 is in the process of crossing the diamond, will the derail set or 
will it remain opened until the car clears the block?
	6)--	What would the derail signal show:
		A)--	before the derail is set?
		B)--	after the derail is (activated to be) set but 
with the opposing block already occupied?
		C)--	after the derail is set and it is clear to 
continue?

	All of the above remained until the end of PRCo days.
	The diagram also shows a 3-light signal for the inbound switch on 
the valley lines to turn outbound to the hilltop lines around the admin 
building and is labeled #4.  Another 3-light signal is #6 and is outbound 
on the hilltop lines to circle behind the admin building.  These two 
signals did not last until the end of PRCo days.  Switch #7 splits the 
interurbans from the other valley lines outbound but does not have a 
signal light.

	7)--	Why are 3-lights needed for setting these switches #4 & 
#6?
	8)--	What did each aspect mean?
	9)--	When were these two 3-light signals removed?

-- 
James B. Holland
       PITTSBURGH RAILWAYS COMPANY (PRCo), June of 1949 -- June of 1953
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