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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

Design and Performance

Track Performance under Heavy Axle Loads

This project has two focus areas. The first provides support for operation of the jointly funded FAST at Transportation Technology Center (TTC). It includes the operation of the heavy axle load train by which performance of sub-grade, ballast, ties, fastenings, rail, and track stability can be evaluated in a controlled laboratory type of environment. As experiments at FAST advance, more emphasis will progress to the second focus area – evaluation of heavy axle load effects in actual revenue service. These experiments will lead to a better understanding of track behavior and degradation under heavy axle loads. The experiments have significant safety implications and will provide the technical support on which to base improvements in safety regulations.

Heavy Axle Loads on Short Lines

Previous research on effects of heavier axle loads has focused on track and bridges with characteristics typical of the main freight routes. Track and bridges on these routes are often of more substantial construction than found on branch lines and short lines, which typically have lower traffic levels and lower operating speeds, and often fall within the lower track classification levels (Classes 1, 2, and 3) of the FRA Track Safety Standards. This effort, being carried out cooperatively with the American Short Line and Regional Railroad Association, will focus on effects of handling heavier loads on short lines and the infrastructure requirements for safely handling these loads at lower volumes and lower speeds.

Track Degradation Model

A computer model for predicting the character and rate of track degradation has been long desired in the railroad industry and research community. Such a model would provide many important benefits, including showing the effect of track defects which occur in combination. Presently, the Track Safety Standards are, to a great extent, based on individual defects, as the ability to clearly define combined effects has not existed. Pieces of the whole track degradation model have been developed over the years, but no model that puts them all together. This effort would focus on putting the pieces together and defining the proper interaction among them. Factors which lead to track deterioration, and their effect, need to be properly quantified, both at the component and system levels as they act in combination. The result of this project will be a complete track degradation model that could be used as a basis for a rational maintenance planning and improved safety. The model will also support the development of performance-based track safety standards.

Upgrading Track for High-Speed Operation

Studies since the 1990’s have indicated that the most practical and economically feasible way of providing high-speed rail service to US corridors is to upgrade existing routes and provide for their joint use by freight trains. Although generally less expensive than all-new construction, upgrading and joint high speed-freight use presents its own complications and challenges. The main complication is providing a track structure that will practically accommodate two uses with such differing requirements; lightweight passenger trains at high speeds and heavily loaded freight trains at slower speeds.

This project focuses on two tasks: roadbed rehabilitation, and track structure design. One issue in a successful upgrading is the extent of roadbed rehabilitation required and method for accomplishing it. Another is building a track structure on the roadbed that will provide the precision surface and alignment required for high speed service, while at the same time, withstand the heavier loads of freight service without experiencing rapid deterioration or requiring constant maintenance. Results from this project will lead to the development of:

  • General criteria for determining the extent of required roadbed rehabilitation
  • Methods for assessing roadbed rehabilitation requirements at each site
  • Design criteria for track which will accommodate high speed while withstanding heavy loads
  • Methods to evaluate track designs specifically intended for high-speed track upgrade.

Alternative Track Designs

The demands on conventional track structure have greatly increased, as heavier freight car weights are requiring greater load carrying capability while higher speed commuter and passenger trains are requiring tighter tolerances for surface geometry and alignment. This project will focus on the development of track structure designs that can better accommodate higher loads while retaining the precision surface and alignment required for higher speeds. Examples of alternative track designs include slab track and embedded rail track, which do not incorporate ties or conventional ballast sections.