The National Academies

Transit IDEA J-04/IDEA 41 [Completed (IDEA)]

Track Geometry/Design Testing for Transit Applications
[ TCRP J-04 (Innovations Deserving Exploratory Analysis--The Transit IDEA Program) ]

  Project Data
Staff Responsibility: Harvey Berlin

This project developed and tested a concept to determine actual track geometry alignment and cross level in sharp curves and turnouts in rail transit systems. The improved track geometry testing system would utilize the current track design or a “best fit” track design as a baseline for testing rail rapid transit and light rail transit track.
This concept would provide transit systems the ability to accurately identify track geometry defects based on their track design, thereby reducing maintenance time and cost. Transit agencies could also benefit by utilizing the “best fit” track design data generated by the track geometry system as an alternative to improve their current track design.
Track classification standards in sharp level curves and turnouts cannot be defined using the industry’s current geometry testing methods. Therefore, during an automated track geometry test, this type of track is not properly classified, and required  maintenance may be ill-defined and possibly overlooked. When using conventional methods of track geometry testing, the track design criteria are not considered. Automated track geometry tests using original design criteria or calculated “best fit” designs would provide accurate results for evaluating track alignment deviations. Evaluating current track conditions and managing these conditions on rail rapid transit and light rail transit systems could be greatly improved if this concept is proven and implemented. Time and costs currently incurred by transit systems in evaluating and managing their track could be significantly reduced. This would improve the efficiency of the track evaluation and of tamper maintenance, which would enable the transit agency to focus its time and efforts on actual track problems, contributing to improved track safety.

Planned Investigation

The Massachusetts Bay Transportation Authority (MBTA) and the Washington Metropolitan Area Transit Authority (WMATA) have participated in this project, including field testing on their tracks. The investigator established agreements with the participating transit systems to utilize geometry data gathered on their respective systems. A software routine was developed to scan the geometry track data and determine the location of curve points. Curve data were selected from the database using the curve point identification procedure developed in the previous software routine. Semi-automated curve designs were developed from the manual curve designs. The curve design model was tested.

Project Results

The project has been successful in defining a continuous analytical function of the "desired curve" that can be made to best fit the measured track geometry curve and serve as a model for track alignment and crosslevel corrections. It has been shown that the desired track is not always a theoretical mathematical model but is rather more complex. The effort has developed a method whereby a digital foot-by-foot description of the regular safe accepted track configuration can be computer generated from automated track geometry measurement data. The process finds the exact position of curve points for the curve model. During the automated search for a solution, the half throws are minimized to within expressed limits. The process therefore provides valid track geometry exceptions as well as tamper input data for correcting the exceptions.

The project results include finding solutions for all 16 curves on a section of track. The tools developed for solving these curves prove that the basic model and concepts for automating the solutions are valid. Design engineers can do the selection and application of these tools manually, or they can be automatically applied in standard sequences as manual applications become routine. To date, two fully automated sequences have been found very useful and further extension of the automation is anticipated based on the elementary tools provided to date.

One challenge remaining to be solved is the synchronization of curve design data with each future geometry test. In theory, the model and the measurements must be located to the nearest foot. In practice, it has been shown that some curve point locations may shift with the seasons. Fortunately, curves in tunnels and complex trackwork do not move and can be used for automatic location detection.

Avenues of further investigation could include (a) making seasonal models of the track design to accommodate seasonal changes in the acceptable track configurations, (b) comparing the model curve points with the original design charts, and (c) proving in practice that the tamper data provided can be synchronized to eliminate the exceptions.

Product Payoff Potential

The method used in this project has been to model the existing track construction as the accepted design and to calculate the deviations from that design and restore the track to its accepted condition with automatic equipment. This is the process used to eliminate false exceptions in geometry reports and to generate valid input data for tamping and lining machinery. Fully implemented, the process can provide automatic location detection of track geometry measurements to the nearest foot. This method would improve the efficiency of rail transit track evaluation and of tamper maintenance.

NTIS # PB2008-101506.

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