Harris Tower Restoration by the
National Railway Historical Society (NRHS) - Harrisburg Chapter


Photos #1 to #8 by John Fryer. Text by Dan Rapak.
Photos #9 to #11 by Dan Rapak. Text by Dan Rapak.
Photos #12 and #13 by Linda Warner.  Text by Jeff Warner.

Click on thumbnails below for larger picture.

Photo #1 - Interlocking Machine
Built by Union Switch and Signal Company for the PRR in the 1920's, the machine contains 113 levers which controlled the track switches and signals for train movements in the vicinity of the State Capitol Building in Harrisburg, PA. Harris Tower was so busy that at times there were three men working the desks and two levermen setting the routes.
Photo #2 - Model Board
View of the model board at Harris Tower in the process of being restored. The model board consists of a diagram of the track configuration in the Harris territory and showed the operators the location of all trains, whether signals were cleared or at stop and whether power was applied to overhead catenary on any given track. To do this, the board contained over 400 indicator lamps. The interlocking machine and model board are being restored to their 1940's condition when Harris was at its busiest.
Photo #3 - Comm Panels
Two of the four communications panels used by operators at Harris. These panels allowed the operators to communicate with operators in other nearby towers, with the dispatchers and others. The panels also allowed the operators to monitor the "block wire" over which all tower operators reported trains passing through their territories. It was in this way that the operators at Harris would know trains were approaching their territory and on which tracks. Note Western Electric telephone operator's style headset on top of right hand panel box.
Photo #4 - Bars and Dogs
Harris Tower Interlocking Machine shown with top cover removed revealing locking bars and dogs. It is this system that provided the mechanical interlocking within the machine to prevent conflicting routes from being set up. This and the photographs below proceed from the top, front to the bottom, rear of the machine.
Photo #5 - Lever Bars and Latches
With their access panel removed, the locking mechanisms controlled by the locking magnets at the top rear of the machine can be seen. The square bars run from the levers at the front of machine (top of this photo) to these latches in the rear. When the locking magnets engage the latches, the levers cannot be moved. (The magnets are not visible in this photo as they are below the base plate but can be seen in Photo #7.) There are three locks on each lever controlling a track switch and one lock on each lever controlling a signal.
Photo #6 - Roller Switches and Locking Magnets
Rear of interlocking machine with cover removed revealing roller switches and locking magnets.
  Photo #7 - Locking Magnets
Close up view of locking magnets, also referred to as indicating magnets. These magnets provide an electrical means of preventing individual levers from being thrown. In addition to the mechanical interlocking provided by the locking bars and dogs in Photo #4, this electrical interlocking prevented levers from being thrown until track switches had lined and locked properly and until signals were displaying properly. They also prevented levers from being thrown when their associated tracks were occupied.  
  Photo #8 - Close up of roller switches
Close up view of the interlocking machine's roller switches, located in the rear of the machine. These rollers are made of rubber and are mechanically connected to the operator's levers by a system of gears and cams. The rollers rotate as the levers are moved. Copper bands are attached to each roller to create a customized set of electrical contacts for each individual lever. The contacts then controlled the actuation of the signals and track switches on the railroad physical plant. Although each roller can accommodate up to 36 contacts, in some cases even this is not enough for a plant as large as Harris. In these cases, two or more rollers are mechanically tied together and rotate simultaneously.  
  Photo #9 - Model Board
The model board at Harris is being restored to its early 1940's layout. It was during this time period - the War years - that Harris handled the greatest number of trains. It was also during that time that the territory was its largest and most complete. The restoration is being based on actual interlocking diagrams and track blueprints from that era. Photo 9 shows part of the model board restoration. The section shown is in the process of being sanded and painted. The white tapes, some of which are hanging to permit sanding, are used to mark the tracks on the board. The holes are the mounting locations of the various indicator lamps for track occupancy, signal indications and catenary power. The bell on the right alerts the operators when a train arrives on territory from the west (from Rockville) on Track 1.  
  Photo #10 - Model Board
Photo 10 shows a "yet to be restored" section of the model board. Signal numbers and track numbers can be seen here. Note the rectangular symbol for the location of Harris tower itself. Inside the symbol is a horizontal line and a dot. In standard signal notation, the line shows the location of the model board relative to the tracks. The dot shows the position of the operator. As the symbol indicates, in the case of Harris, when the operator is facing the model board his back is toward the tracks outside.  
  Photo #11 - Testing
Harris is being restored as a "hands on" exhibit for school students, railroad buffs and anyone else interested in learning how railroads operated in days past. Our goal is to have visitors actually operate the interlocking machine and other equipment to learn first hand what running a railroad was like at a time before the advent of modern CTC operation. To accomplish this goal, the interlocking machine, model board, communications panels and other devices will be connected to a computer. The computer will then simulate train movements over the Harris territory based on train schedules from the 1940's. A 1940's vintage Teletype machine will print out consist reports (220 Reports) when the virtual trains leave their terminals. Train progress will be monitored by audio announcements from other interlocking towers over the "train wire" speaker system in use during that the time period. Trains will arrive on territory and it will be up to the visitor to operate the interlocking machine to route the virtual trains to their proper destinations. The difficulty in this approach lies in finding a way to interface a 1920's vintage interlocking machine with a 21st century personal computer. Our approach is to use an industrial controller. An industrial controller is a device that is intended to run an assembly line in a factory. Its purpose is to read sensor switches, electric eyes, pressure switches and so on, and then control motors, conveyor belts and other devices that are part of the assembly process. In the case of Harris the controller will read the positions of the levers and push buttons on the interlocking machine and communications panels and control the model board and other indicator lights according to the simulation being run on the computer. Photo 11 shows a portion of the controller undergoing testing and programming. As one might imagine, custom software has to be written for the Harris simulation. This photo shows a part of that process.  
  Photo #12 - Restored Model Board
A view of the left hand side of the restored model board taken in 2008. 
  Photo #13 - Restored Model Board
A view of the right hand side of the restored model board taken in 2008.