The National Academies

TCRP D-22 [Active]

A Frog Design Primer and Research Roadmap

  Project Data
Funds: $300,000
Staff Responsibility: Mariela Garcia-Colberg
Research Agency: Cross-Spectrum Acoustics, Inc.
Principal Investigator: Shannon McKenna


The frog is a component of special trackwork where one rail crosses another. Openings called flangeways are provided in standard frogs so that the flanges on the vehicle wheels can pass through. When the wheel passes through the open flangeway at the point of the frog, the wheel tread and frog wing rail surface locations produce high impact forces, noise, and vibration. When frogs must be located near noise- and vibration-sensitive land uses, they are often identified as having impacts during the environmental review process and require mitigation. Flange bearing frogs are typically used in standard light rail track on streets. 

Low-impact frog designs can reduce noise and vibration levels. However, there is almost no publicly available data on how effectively low-impact frog designs reduce noise and vibration levels, their longevity, and their maintainability. As a result, many agencies are hesitant to adopt new frog designs.

A primer and research roadmap are needed to inform rail transit agency personnel, agencies, and rail designers on the following questions:

  • How do frogs perform? What is their function? How long do they last? How are they maintained?
  • How have frog designs evolved over time?
  • What are the physics and mechanics of frog performance?
  • What is a low-impact frog design?
  • What is the status of current practices for maintenance and condition assessment, including replacement criteria?
  • What is the status of research worldwide of frog impacts?
  • What can be done to reduce noise and vibration at frogs?
  • American Railway Engineering and Maintenance-of-Way Association (AREMA) designs for frogs and switch points conform to Federal Railroad Administration (FRA) safety standards. How do transit designs for frogs and switch points differ?
  • What is the performance history of current rail transit frog designs for noise and vibration reduction and life cycle?
  • Is there a recommended test method for measuring the noise and vibration generated by frogs?
  • Frog designs include traditional, movable point, and conformal frog designs. How might improvements in performance be achieved for each design?
  • What alternative designs are available?
  • What informs the choice of materials used in the manufacture of frogs?
  • How do the materials installed beneath frogs affect noise and vibration performance?
  • What are effective maintenance practices for frog performance?
  • Based on data on existing frog types, are existing noise and vibration prediction models accurate?
  • The wing rail and point of frog are where impact is generated. How might such impacts be reduced in new designs? How might other components of the frog system be improved to mitigate impacts?
  • Where are the physical stresses transferred if a design reduces vibration?
  • Each material has different stress effects. How can one determine the ultimate limits for frogs and the materials installed beneath them?
  • What is the role of Environmental Impact Statements on considerations for alternative frog designs?
  • How might an agency conduct frog lifecycle analysis? What associated tools are available?
  • Does noise and vibration change significantly from new to the maintenance wear limit?


The objectives of this project are to develop (1) a frog design primer and (2) a research roadmap. 

The primer is to provide guidance to transit agencies on how to select appropriate frog designs for noise and vibration mitigation and how to maintain good noise and vibration performance through effective maintenance practices. 

The research roadmap should be built on analyses of frog systems, informed by current practices and a literature review focused on the reduction in noise and vibration provided by alternative low-impact frog designs. The research roadmap is intended to be used by the rail transit community to focus its efforts to foster, support, monitor, disseminate, and implement research on frog system design. The roadmap will build upon existing research and will be informed by outreach to the active rail design, procurement, operations, and maintenance practitioner community. In addition to identifying research gaps and prioritizing research needs, the roadmap should foster collaboration with standards development organizations such as the American Public Transportation Association (APTA) and AREMA.


The research plan will describe appropriate deliverables that include the following (which also represent key project milestones):

  1. An Amplified Research Plan that responds to comments provided by the project panel at the contractor selection meeting.
  2. An Interim Report and panel meeting. The Interim Report should include the analyses and results of completed tasks, an update of the remaining tasks, and a detailed outline of the final research product(s). The panel meeting will take place after the panel review of the Interim Report. The Interim Report and panel meeting should occur after the expenditure of no more than 40 percent of the project budget.


The final deliverables will include:

  • A frog design primer and research roadmap.
  • stand-alone technical memorandum titled “Implementation of Research Findings and Products”.
  • report with the following:
    • Documentation of the research activities;
    • Key Findings; and
    • Other topics identified during the project.


STATUS: A research agency has been selected for the project. Research in progress.

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