PENNSYRR.COM by Jerry Britton

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The Pennsylvania Railroad had operated a specially designed car constructed on a flat car. It's purpose was to accurately measure the distance above and/or adjacent to the tracks of bridges, tunnels, stations and rock cuts, etc.

The demaind for increased speed to shorten travel time in both present day industry and the business world has caused the railroad to provide more clearance for movement of equipment. The trend to larger equipment such as locomotives, passenger & freight cars and larger loads in open top cars has made the gathering of clearance information an area of growing importance. The Pennsylvania has spent millions of dollars to increase clerances for handling traffic. In the 1950s alone, the Panhandle Division tunnel project between Pittsburgh, Pa., and Dennision, Oh., cost over $8 million.

 With the increased speed and more frequent schedules, in addition to the vast increase in traffic experienced during World War II, it became necessry to develop a means of measuring clearances of structures along the right of way faster and more efficiently. This was not possible with the open type clearance car that was operating prior to the 50s. Therefore the open car had become obsolete and was dismantled in mid-1950.

 The Pennsylvania Railroad was able to accomplish the challenge of more accurate measurements with it's new Clearance Car #497125. The car was designed by the Mechanical Department and the Chief Engineer's Clearance Department. It was built at Pennsy's Altoona Works in Altoona, Pa., in 1950. The first test run was made over the Middle Division on November 7, 1950, during which it measured the Spruce Creek tunnel (22 miles est of Altoona). The car used in the construction of the clearance car was a former inspection car of the P68 passenger type of the time.

The car is divided into five compartments. The head end or front is the Template Room where all the measuring instruments are located. On the exterior of the car there are a total of 126 measuring instruments called feelers. The Template Room is the location of the gauges that record the movement of each feeler as the car moves through a tunnel or bridge, etc. The feelers are divided into four groups: 1) the curved template is called the Horseshoe, 2) the Main Templates, one on each side of the car, 3) the RIght Foot Template, and 4) the Left Foot Template.


It is adjustable and can be raised one, two, three, or four feet which permits measurements of 17' to 21' above the top of the rail. When the Horseshoe is down, normal or travel position, the lowest feeler, #30 is 8' above the top of the rail. At this point the Horseshoe with 60 feelers curves over the top of the car on a five foot radius. The lower three feelers of the Horseshoe on each side are 6" apart. When traveling between assignments, the Horseshoe is in a down position and all feelers are in a closed and locked position.

Main Templates

There are two main templates in fixed positions, one on each side of the car. The lowest feeler is 2'3" above the top of the rail and the highest feeler is 11'6" above the top of the rail. The lower 14 feelers are 3" apart and thre remaining 12 feelers are 6" apart.

Foot Templates

There are two foot templates, one on each side of the car. Each has 7 feelers which are 3" apart. These templates are hydraulically controlled to raise the assembly partially up into the car while in transit and lowered when ready to perform measurements. When in the down position, the bottom feeler is 6" above the top of the rail and the top feeler is 2' above the top of the rail. The foot templates are raised up into the car in transit to prevent striking objects along the right of way. Prior to raising the feelers must be closed and locked.

Operation of the Car

The car is entered through the template room at the front of the car. At first sight, the controls and gauges for each feeler seem quite complicated but are quite easy to comprehend. The instruments consist of three main parts: 1) feelers connected to an outside gearbox, 2) a length of teleflex cable which passes through special brass tubing, and 3) the indicator quadrant with gearbox and magnifying glass. The feelers which are outisde of the car are 36" long and are made out of 1/2" aluminum tubing with a tip of 6" hardened tool steel on the end. This insures longer wear and more accurate measurements.

Each feeler is attached to a shaft extending from the outside gearbox. Both shaft and feeler fittings have serrations which allows for a more delicate adjustment on dead center. The feeler is secured to the shaft by means of two washers, locknut, and clamp bolt. One washer is made of spring steel, slighly cup shaped with protruding legs bearing against a fiber washer. The purpose is to obtain proper friction so that the feeler will not swing back too freely or be too rigid when making contact with structures. The flexible cable which passes from the outside gearbox, through the brass tubing to the gearbox on the indicator quadrant is of special design. It was developed during World War II for aviation and marine controls. On the outer circumference of the quadrant is a white scale with black numbers with increments of 1/8"from 9" - 36". The scale is calibrated so that it's readings indicate the exact clearance measurement taken by the feeler in that position. This is all encased with an opening over which is attached a magnifying glass with a hair line marking on the underside, This indicates the proper position for reading the scale. Also atached to the quadrant indicator is a handle for extending or retracting the feeler as required and a stop/hold for locking the feeler in a closed position.

The car has an intercom system with two-way speakers and head phones in the template room and a two-way speaker in the recording room for constant communication between the two rooms during its operation.

From the rear of the template room you can access the observation dome by means of two small ladders on each side. This is to allow for inspection of overhead structures and tunnels. A seat for this purpose is provided on each side of the dome.

The next compartment consists of a stainless steel kitchen with an electric refrigerator, sink with running water and a stove that burns charcoal, wood or coal. This is on the right side when facing the rear of the car. On the left is the washroom which has three wash basins with cabinets and mirrors with electric outlets above each one. There is also one shower room and a private toilet room. Continuing on to the rear of the car, we enter the sleeping compartment with standard Pullman type upper and lower berths. This section also has lockers for each man's personal belongings and storage for bed linens.

Following this we come to the office area. The operation of the car is directed from here. It is equipped with a desk where the readings of each feeler is recorded on a clesrance diagram. This information is received over the intercom from the two men in the template room. This compartment also contains a table, chairs & filing cabinets in which track charts, maps and current clearance diagrams are stored. This same area is also used as a lounge and dining room.

A diesel generator is located in the last compartment of the car and is used to power ak electrical equipment. A ladders is located in this room directly over the center line of the rear truck for access through a hatch in the ceiling to the rear template. It allows for measuring overhead bridges and other structures which are more than 21' above the top of the rail. The measuring is done by means of a telescoping gauge that can be extended to the underside of a bridge or other structure. At that point the car is stopped and the gauge extended to the underside of the structure being measured. THe gauge is graduated for direct reading in feet and inches above the top of the rail.

The clearance car is moved over the railroad in regular passenger service when traveling between headquarters and working locations. It is not a self propelled car and when taking measurements, it is moved with a lotomotive and rider car for the train crew. When measuring, the clearance car is operated as a special passenger train.

t the begining of a day's work, the first structure to be measured is located on a track chart in the recording room. THe mileage, location and tyope of structure to be measured is obtained from the structure's own clearance diagram. It also indicates how the templates and feelers will be set and which ones will be used. If the Horseshoe is needed, the setting will be determined from the clearance diagram. This information is then relayed over the intercom to the men in the template room. As the train approaches the structure, it will slow to approximately 5 m.p.h. and stop about two car lengths from the structure to be measured. At this point, the crew in the template room will make all of their settings and extend all feelers that are necessary, The train will then move through the structure at a walking speed pace. As the car moves through slowly, the feelers striking the structure are brushed back which in turn form a contour of said structure. When clear of the structure the train will stop and the crew will record the measurements on a clerance diagram. The scale on the diagram is 1/2" - 1'. Each structure measured is recorded on a single diagram and a separate diagram is used for each track.

The clearance car is usually operated by a crew of three men under the direction of the Clearance Engineer. Each man has specified duties, two in the template room and one at the recording desk. The two men in the template room operate the templates, feelers and horseshoe while observing the structure being measured and report any unusual conditions. The man in the recording room plots the measurements on a clearance diagram while also recording unusual conditions and keeps a record of the date and the mileage of the car and all structures measured.

The car was usually out on the system measuring from April to late October. THe rest of the year the crew was in the office compiling the field notes. The individual structures were then compiled on a single sheet showing all structures between any two junctions or interlockings. A sheet was also made for each track. Copies of these sheets were made and forwarded to the Regional and Division Engineerm, M of W and the Transportation Department's Clearance Bureau. The Clearance Bureau does all the routing of high and wide loads for the PRR.

This car reduced more than 75% of the actual measuring and recording time over the previously used open flat car. Upon completion of recording and measurements of a structure which takes only minutes, the diagram is complete and the clearance of a structure can be determined immediately. This car was also leased to other railroads since the PRR owned the only car of this type. It was leased to and traveled over the RF&P, Virginian, Norfolk & Western, Rock Island, Long Island, and the Milwaukee Road.

The above article accompanied brass replicas produced by Railworks.

Two page article that was in the February 1954 of Pennsy magazine.
Pennsy 54FEB 10 A Pa Pennsy 54FEB 11 A Pa


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2011 photo by R. A. Lowry. Geigertown, Pa.:PRR 497125 Clearance Car Img 4075 01  2011 photo by R. A. Lowry. Geigertown, Pa.:PRR 497125 Clearance Car Img 4127 01  


A HO scale replica of this car was produced in brass by Railworks in 2000: