Automatic interlockings at railroad crossings-at-grade

[NW Mailing List]

Date: Mon, 6 Aug 2007 09:02:45 EDT
From: NW Mailing List <nw-mailing-list at nwhs.org>
Subject: Re: winston-salem district
To: nw-mailing-list at nwhs.org


Jeff-
Let's get back to the "automatic" feature that was, 
and apparently still is, incorporated into the
interlocking  at Walnut Cove.  The components of the
interlocking  make a decision based on one factor --
which train hits  the approach circuit first.  There's
no bias to  railroad.  There's no consideration to
priority.  There's no  consideration to which train
has the most tonnage.  Direction  doesn't matter.  The
approach circuit is an arrangement of signaltry that
detects an approaching train.   Apparently the
approach circuit for northbound trains coming  to
Walnut Cove is in the vicinity of MP 113.   When the
train  activates
the approach circuit, the components in the relay 
case at Walnut Cove start scanning.   Is there a train
on  the bisecting route?  In this case the bisecting
route had  been Southern's Winston-Salem Division.  
Is there a train in the block ahead ?  Once convinced
that the route is unobstructed, the home signal ( at
MP 108.8) will clear.   Only
then will the aspect of the distant signal change to
be more favorable.
 
When NS abandoned the track Greensboro to Rural Hall,
the bisecting route was eliminated, but apparently NS
only  modified the interlocking.  When a northbound
shunts the approach circuit, the interlocking
continues to "search"  for trains in the block toward
Belews Creek Jct., and maybe for those Winston-Salem
Division trains that'll never come.

Harry Bundy



August 6, 2007

Harry is right, in my opinion.  When I was working on
the Brooklyn District of the former Wabash, the
single-track Penn Central (ex-Peoria & Eastern?)
crossed the double track N&W at Litchfield, Illinois. 
The Penn Central abandoned the line on either side of
the crossing, but the diamonds and signaling were
intact and fully operational.  The rationale, I think,
was that it was easier to leave it all in place than
it was to make changes to the signaling and get
Federal Railroad Administration approval for the
changes.  I don't know if it was true then and because
of the high maintenace cost of diamonds, maybe they
were eventially straight-railed --but with the signals
still in operation.

I always thought it made for an interesting picture to
view the former PC right-of-way barren up to the
diamonds, with a stop-and-stay signal displayed. 
Maybe it's still needed for the Polar Express when it
makes its midnight run....

Best wishes,

Frank
f_scheer at yahoo.com