TTCI weighs in on TADS and TPDs

Railway Age, April, 2004 by Keith L. Hawthorne

I've read with interest Tom Canter's comments in "Point of View" in the February 2004 Railway Age. While I'll leave others to comment on his other points, I would like to address his comments regarding acoustic bearing detectors and truck performance detectors (TPDs).

Transportation Technology Center, Inc., is, as far as I know, the only North American producer of modern-generation acoustic beating detectors. Our Trackside Acoustic Detector System (TADS) has had an excellent record of flagging bearings with serious internal defects. We feel quite comfortable stating that TADS is virtually 100% accurate on cars with correct and properly placed AEI tags.

As to the comment that TADS systems "miss others that are defective," I have no idea how Canter, or anyone else, would know this unless they had specific knowledge of burn-off derailments with bearings that TADS had recently said were good. We are aware of no such occurrences. Of course, there are some bearing defects that TADS alone can't find (and doesn't claim to find) because they have no repeatable and consistent acoustic signature; loose backing rings and loose cap screws are two examples.

As to TPDs, Canter notes that TPDs "can flag cars for which a defect cannot be found." This should not be given a negative connotation. The ability to find combinations of conditions that add up to excessive lateral forces is exactly what the Truck Performance Research Consortium intended when the first TPDs were developed. While such conditions may not be condemnable individually, when they appear in combinations such as hollow wheels, tight sidebearings, and dry center bowls, they may well pose very serious derailment risks.

The lateral forces measured by TPDs are a clear indication of an undesirable or unsafe condition depending on their magnitude. These are just the types of issues now being addressed by the Association of American Railroads' Stress State Task Force.

Keith L Hawthorne

Vice President-Technology

Transportation Technology Center, Inc.