After studying the available technology, it was decided to build an automated video system that would enable clearance engineers to link video with computer-assisted drafting technology. Construction of the CMV-1 began with the installation of an inverter, high-output alternator and two large diesel batteries. This was essentially the power supply which would change 12 volts DC to 120 volts AC.
The video components, consisting of a video monitor, a ¾ inch tape player, a camera-control unit and a console control unit are housed in cabinets.
In order to obtain the desired field of view, the camera and a special wide-angle lens had to be located approximately 21 feet from the image. This meant that the camera had to be supported above and behind the roof of the hi-rail vehicle. So, a special crane-like device that can lift the 25-pound camera and hold it securely in place was designed and mounted on top of the vehicle. The CMV-1 is able to measure clearances after dark, in foul weather and requires only one operator.
Among the advantages of the video are that clearance engineers can evaluate each cross section of a particular structure relative to its proximity to the track. Whether the track is on the curve, spiral or tangent affects the clearance profile of the structure. Engineers can also determine exactly what needs to be done to a particular structure to improve line clearance.
Another advantage of the video system is the ability to perform structure inspections. If desired, the structure being video taped can be illuminated by several high output exterior lights on the vehicle and inspected for the defects from the office by «blowing up» portions of the video tape.
This system is up-to-date and accurate enough to calculate distances for the safe passage of trains on adjacent tracks.
T e x t 2
When field supervisors determine that the use of geotextiles is warranted. They make certain that they’re installed deep enough in areas that may be undercut. Generally, that requires 12 inches of ballast and six inches of compacted subballast material be placed on top of the cloth. The material, which extends 10 feet beyond either end of the crossing, is laid on a sloped crown to facilitate drainage. Six inches of perforated pipe are aiso installed on each side of the crow.
Also standard when rebuilding a crossing is to use 78-foot rail lengths. Rail on branch lines is upgraded to 112-or 115-pound rail; mainlines get 132- or 136- pound rail. All rail joints within 10 feet of a crossing are welded.
In addition to the general BN guidelines, maintenance personnel on the Western Division have assembled a manual of grade-crossing renewal practices. The many items dealt with include:
– Fabric: lay soil fabrics after the grade has been leveled with a slope toward the corners; cover the fabric with enough subbalast to protect it.
– Anchors: The crossing should have a solid pattern; use enough anchors to standardize the pattern away from the crossing.
– Ballast: fill to the proper lift, tamp tie centers and fill tie cribs.
– Ties: Use enough (No. 5 hardwood, minimum) ties to extend 10 to 15 ties beyond each end of the crossing.
– Prates: Use the largest size available for the weight of the rail and type of crossing.
– Rail: Use the largest size that is appropriate; use enough rail so that there are no joints within 20 to 30 feet of the crossing.
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