Todd's Railfan Guide to the drawings for
Baltimore MD



In General

Carroll Interlocking in Baltimore MD was perhaps the last place in the United States that could boost a FULL B&O style CPL signal.  And to boot, the signal was upgraded to this status about 2 or 3 years before it was replaced by colorlight signals in 2012.

Myself, Mike Brotzman, and Michael Watnoski went out one day to take pictures, and we happened to catch Carroll Interlocking just at the right time, as there was a dumpster full of stuff from the changeover, including what remained of the drawings for the CPL interlocking.  Some were torn, some had coffee and sugar packets on em, and some were pretty well faded.  And so it goes.....

The pictures below of the drawings are just that, pictures I took of the drawings before Michael took possession of them.  I didn't have either the patience or money to scan the drawings at 2 bucks a sheet, and then wait or come back to like Staples or Office Depot to get what I got below.  Yeah, I know the quality isn't there, but I'm not after reference or library quality.  Despite the fact that the pictures are not linear, they still tell you the story.  If someone wants to have a good copy of the prints, it will cost you $2.50 a sheet.  Also, only about 2/3 of the sheets we yanked out of the dumpster are presented here.  Most of the pictures have sufficient detail to read all of the printing and schematics, maybe not the clearest, but it will do.

Now the rest of the story.  Prints such as these only tell a very small part of the story.  Even if you had all of the drawings of hte interlocking, it would still not tell you the logic or principles of design for the interlocking.  It would take weeks (probably) to sit there and decipher the drawings to figure out what conditions cause what indications on any one signal, and there are (I believe) 9 signals in this interlocking (51L and 51R are around the corner (at Washington Blvd) and not seen in any of the photos).

If I can use a comparison against one of the things I work on: an ASR-12 airport radar system.  Even if you had all of the drawings of the radar system, you still would not be able to tell how the thing works... same thing with the interlocking here at Carroll, or anyplace for that matter.  Redundancy would not be readily apparent, nor would the fact that the "short" transmitter pulse for close range targets is sent out immediately after the "long" pulse used for distant aircraft, for it listens for the returns of the nearby airplanes while it is waiting for the returns of the distant targets.  There is also a slight modulation of the two pulses for near and far, that tells the receiver which algorithm to send the received info to.  Drawings don't tell the whole story.

I went to the trouble of substituting larger size photos for the thumbnails, in order to make it a little easier to see what you are clicking on, as there are roughly 90 pictures, some may be important to you, others may not, this took an extra hour and a half to do.....  Average size for the full size pictures are around 2 to 4meg jpegs.

Pictures and additional information is always needed if anyone feels inclined to take 'em, send 'em, and share 'em, or if you have something to add or correct.... credit is always given! Contact info is here


  Cantilever signal bridge at #1, with the full CPL on it (left)

  #1, #2, #3, and way off beyond the interstate, #7

 After CPL replacement

  AFTER :-(

  One of the new colorlights has been installed across from the CPL in this shot































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EW 11/2/2013
Last Modified 02-Nov-2013