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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Inspection Techniques

Rail Defect Detection

This effort is aimed at producing better and faster methods for detecting internal rail and joint bar defects and developing automated methods for better and more consistent interpretation of rail defect measurement data. Plans include expansion of a Rail Defect Test Facility (RDTF) at the FRA Transportation Technology Center (TTC). The RDTF is a track containing a wide range (both type and size) of well-documented internal defects. Additional samples will be installed to include rails that have both internal and surface defects as well as other examples of defects or defect combinations that have proven difficult to reliably detect. The RDTF will be used to accurately measure the performance of existing detection methods, and then, to diagnose detection deficiencies. From these evaluations, improvements in detection methods and in interpretation of detector measurement data can then be proposed and developed. Improved defect management and repair practices can also be formulated.

Alternative Techniques for the Detection of Broken Rail or Track Hazards

This project will assess the application of new technologies other than those normally used for the detection of rail flaws. Special emphasis will be placed upon the feasibility of a train-mounted device for detection of broken rail or other hazards ahead of a moving train. Currently, track circuits for signaling also provide a secondary function of detecting broken rail. However, about half of the railroad mileage does not have signal circuits and is otherwise not equipped with a broken rail detection system. In addition, signal circuits are not infallible in detecting broken rails. Even where signal circuits are present and a rail breaks without the presence of a train, signals will not always show Stop if a rail breaks over a tie plate. Initial efforts will focus on broken rail detection, followed by track hazard detection in general.

Longitudinal Rail Stress Measurement

The ability to measure internal rail stresses is essential for accurately predicting track buckling potential and for prescribing the most effective remedial action to prevent buckling. This capability has long been desired in the engineering world and the FRA will continue pursuit of this objective. To date, track-mounted methods have shown some success, but what is needed is a method to make these measurements continuously along the track at moderate-to-high speed. This, along with on-board rail integrity detection, is a component element of Intelligent Railroad Systems. 

Track Gage Widening Strength

One of the major causes of derailments is widening of the track gage due to weakened ties, thereby allowing the pair of rails to spread too far apart from each other under load and causing the wheels of a passing train to drop between the rails. In response to this recurrent problem, the FRA developed the Gage Restraint Measurement System (GRMS) to measure track gage-holding strength continuously along the track. The GRMS has demonstrated superior ability to detect weak track locations due to unsatisfactory tie conditions.

Current gage restraint measuring capabilities tend toward opposite ends of the scale – a method suitable for measuring up to 200 miles per day on a production basis, and a simple manual method suitable for measuring selected spots. The next focus will be on filling in the gap by providing a reliable method for measuring shorter distances (5 to 50 miles) in a more efficient and cost-effective manner. This method will make application of GRMS more practical on short line railroads, through yards and sidings, and on branch lines of major systems. FRA will also continue operation of its production GRMS system to provide data to support decisions on waiver requests and for jointly sponsored testing with the railroad industry. It will also be a major source for track data for the comprehensive track degradation model development project. Results from this testing, along with the track degradation modeling project, will help in the development of performance-based track standards for track gage and ties.

Vertical Track Support Measurement

Vertical deflection measurement can enhance the railroad industry’s ability to maintain safe track structures by locating areas of inadequate or non-uniform vertical support. This weakness may also indicate poor soil load-bearing capacity in the base or sub-base region of the track structure.

FRA research has already produced a family of instrumented railcars capable, at normal track speeds, of measuring track geometry parameters against Federal Track Safety Standards, and the GRMS, which measures the ability of track to maintain gage to preclude wide gage derailment. New developments in technology in the areas of both data acquisition and processing make it now possible to consider the inclusion of track vertical deflection measurements. A multiphase research project has been formulated under the Track Research Program in this important area of track modulus and related measurements. The initial phase work on feasibility study has been completed and has confirmed the technical feasibility of the proposed Vertical Track Deflection Measurement within an acceptable level of accuracy. A prototype measurement system was designed in 2000-2002, with fabrication and field-testing in 2002-2004.

Automated Inspection of Roadbed 

Track subsurface layers (ballast, sub-ballast, and sub-grade) provide the required support to the track structure. Poor subsurface conditions result in poor track performance as well as excessive and uneven track degradation. Uneven degradation results in costly maintenance and adversely affects track safety.

Since ballast, sub-ballast, and sub-grade layers are beneath the track structure, they are difficult to properly inspect with purely visual methods. Currently, there is no practical method for rapid subsurface evaluation. However, emerging technologies, such as ground penetrating radar or use of sonic or vibration signals, offer promise for developing both improved and automated roadbed inspection capabilities.

Non-Destructive Evaluation (NDE) of Bridges

As freight car weights increase and bridges age, the need for effective, rapid bridge inspection and strength evaluation methods increases as well. The FRA will work jointly with the Federal Highway Administration (FHWA) and the Association of American Railroads (AAR) to investigate NDE technologies that may be applicable in automated bridge safety monitoring. The intent is to pursue techniques that show a high potential for successful adaptation and deployment.