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Database Analysis 81 structure failures also can cause serious accidents. The second most common track-caused haz- mat release accident is track geometry, followed by roadbed problems, and switch and frog prob- lems. Railroads use a combination of manual and automated inspection technologies to detect problems before they become critical, but some are not found and derailments can occur as a result. Overall, the FRA has more than 65 different cause codes for railroad-track-caused acci- dents. This enables a very fine-grained ability to analyze which causes are the most important contributors to hazmat accidents. For both rolling stock and infrastructure, the American Association of Railroads (AAR), FRA, and Class 1 railroads are conducting or sponsoring research and development of better designs, materials, and operational practices that will be more resistant to failure. In parallel, they are also conducting research and development on an array of technologies intended to improve the inspection capability for a wide range of possible defects. 4.6.2 Signal and Communication Accidents caused by signal and communication failure rank last among major categories of accidents and as a cause of hazmat releases. Unlike highways, virtually all railroad operations take place in a highly controlled environment. Specific rules and protocols apply to operation on all portions of the railroad. Communications and signals (C&S) are an essential element of these systems whose purpose is to ensure safe and efficient operation of the railroad. If some element of these systems malfunctions, it may result in incorrect or incomplete information being trans- ferred to or from the train, thereby creating the potential for conflicting track occupancy author- ities or excessive speed. Under these conditions, the consequences may often be a collision or derailment. Railroad C&S systems are thus designed to be extremely robust and embody exten- sive fail-safe elements in their design (i.e., if they fail, it results in a "safe" condition, indication, or message). Consequently, railroad accidents attributable to C&S failures are rare. In a recent study, they accounted for only 3/10ths of 1% of all the U.S. railroad mainline accidents. Never- theless, when such failures do occur, the resultant accidents tend to have high consequences because the outcome will often be a collision or overspeed derailment, thereby resulting in rela- tively large impact forces. If hazardous materials are involved, there is a reasonably high poten- tial to breach the car transporting them and cause a release. 4.6.3 Mechanical and Electrical Failures Accidents caused by mechanical and electrical failure are the second most common major cat- egories of accident cause, and third overall in causing hazmat releases, However, when one con- siders only mainline-accident-caused hazmat releases, they rank second. Railroads operate trains with hazardous materials in the consist, which ranges greatly in number of vehicles and length. The consist is defined as the group of rail vehicles that make up a train. These trains may have less than a dozen cars or more than 150, ranging in length from a few hundred feet to nearly two miles. This has a variety of implications in terms of the occurrence of accidents, and the conse- quent approaches to root cause analysis. With approximately 1.5 million railcars and approximately 800 different owners, railcars spend a great deal of time operating on railroads and by companies other than their owners. Fre- quently, repairs must be conducted on the road by someone other than the railcar's owner. Rail- cars have not generally been subject to programmed maintenance in North America. Instead, railroads and car owners have operated under a philosophy of run to (near) failure. The objec- tive is to obtain as much life as possible from components without suffering failure. Due to the frequent and redundant inspections railcars receive as they move from terminal to terminal dur-