Anybody know the logic the various railroads use in locating defect detectors?
I’m asking because there is a large variance between what the railroads I’m familiar with in Michigan, Ohio, and Indiana have.The NS lines I know about; Detroit/Fort Wayne, and the Chicago Line have them about every ten miles. CN and CSX lines in Michigan have them about every thirty miles.
I’ve seen a couple of wrecks (not just derailments) on the CN mainline through Michigan that have occurred a mile or two before the next defect detector. Could CN have prevented that id they had their detectors spaced ten miles apart rather than thirty, and if so, would it be cost effective considering installation and maintenance costs?
How far apart do UP, BNSF,KCS, and regionals space their defect detectors?
The logic is complex because there are many considerations and many demands on scarce investment dollars. Elements that go into where to invest are all economic at their foundation, and include for a given line segment:
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Annual gross ton miles
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Maximum train speeds
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Concrete ties or wood ties
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Age of the signaling system; where it sits on the replacement schedule
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Presence, type, and quantity of hazmat
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Presence, speed, and quantity of passenger traffic
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Whether passenger carriers will participate in cost
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Presence of sensitive environmental zones, number and population of communities the line passes through
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Method of Operation, e.g., CTC, Form D, TWC, DTC, OCS, etc.
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Bandwidth of existing communication systems, age of systems, etc.
All of these and more go into planning, scheduling, and budgeting for detector installation and upgrades. For example, on new main track in concrete tie territory with 40 MGT per year or more and a lot of hazmat, a dragging-equipment detector may be installed at every intermediate signal (spacing between 4,000 and 12,000 feet) and a HBD every 10 miles. On a line with four trains per day, wood ties, not so much hazmat, a DED may be placed every 30 miles or more. The railroad can justify only so much money and puts it where it gets the best return on investment.
There’s no “standard” per railroad on spacing of DEDs and HBDs that I have ever seen or been apprised of, and if you went out and measured one, it might be as much as result of happenstance as plan – there’s a lot of contingency and history here. We have a lot of discussions about it on new construction, in operations planning, and in maintenance planning. I’ve seen some planning documents and been to some presentations where people have proposed various spacings for various lines in a conceptual sense, but those don’t end up being etched in stone or anything like that.