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Evaluating Frog Design to Minimize Noise and Vibration and Improve Life-Cycle Costs


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, low-impact frog designs are often recommended as a mitigation measure. Reducing the impact forces reduces the resulting noise and vibration levels. Another advantage of low-impact frogs can be reduced maintenance costs and less wear and tear on the rolling stock.

Several resources are available that describe low-impact frog designs that can be used as mitigation measures, but very little data is available on the noise and vibration reduction and reduced maintenance costs provided by the different designs. The Track Design Handbook for Light Rail Transit presents monoblock, flange-bearing, spring-rail, moveable-point, and lift-over or “jump” frogs as alternatives to a standard rail-bound manganese (RBM) frog. The Federal Transit Administration Transit Noise and Vibration Impact Assessment Manual lists moveable-point and spring-rail frogs as a mitigation measure, but does not provide a decibel reduction value for these alternative designs and does not discuss the potential of various low-impact frog designs as noise and vibration mitigation measures. Neither resource discusses the decibel noise or vibration reduction provided by any of the low-impact frog designs, which include monoblock, conformal, flange-bearing, jump frogs, and other potential designs. It is commonly held that moveable-point and spring-rail frogs that provide continuous wheel support through the frog reduce most, if not all, of the noise and vibration increase caused by the wheel impact at the frog point. However, these are costly, high-maintenance items and the Track Design Handbook recommends they only be used when unavoidable. Information on how effective different low-impact designs are at reducing noise and vibration levels would help transit agencies justify using simpler installations, such as monoblock and conformal frogs, which would save on installation costs and maintenance.

There is also the possibility of correlating relative differences in noise and vibration levels to frog maintenance and replacement needs. Changes in noise and vibration levels throughout the life of the frog may be a useful indicator of when maintenance is required and how much time before a replacement is needed. Gathering data on relative noise and vibration increases from frogs at different points in their life-cycle could be used to gauge the need for repair or replacement and ensure well performing frogs are left in service longer and ensure that frogs that are prematurely worn and producing greater impact forces are repaired or removed from services before there are failures. This data could also be used to study the life-cycle costs of the different frog designs. In addition to the noise and vibration benefits of low-impact frog designs, the lower impact forces likely mean longer lifespan and lower life-cycle costs. Other potential benefits include reduced stresses on the rolling stock and allowing higher speeds through special trackwork.


The primary objective of this research is to determine the noise and vibration reduction provided by alternative low-impact frog designs and provide guidance to transit agencies on how to select the appropriate frog for noise and vibration mitigation and what maintenance practices are necessary to maintain good noise and vibration performance. The secondary objective is to study if noise and vibration levels can be used in life-cycle determinations for frogs, such as how much longer low-impact frogs are likely to last compared to standard frogs and if monitoring noise and vibration levels can be used to identify the need for preventative maintenance and extend the life of frogs.


Most new transit lines require noise and vibration mitigation for frogs and any existing systems are replacing worn frogs as part of an effort to bring their systems into a state-of-good-repair, making this an urgent issue for both new and legacy transit systems. The FTA Transit Noise and Vibration Guidance Manual estimates that a spring frog costs about $12,000 and a moveable point frog, which involves elaborate signal and control circuitry costs approximately $200,000, and this cost data is likely out of date. Guidance to identify the most appropriate low-impact frog could save agencies hundreds of thousands of dollars plus reduce life-cycle costs.

No political or socio-economic barriers to implementation are anticipated. The institutional barrier to implementation is the ability to effectively disseminate the guidance to track and noise and vibration practitioners.

Related Research:

Related work was completed for the TCRP Report 155: Track Design Handbook for Light Rail Transit, published in 2012. Related work in Europe was completed as part of the Quiet Tracks for Sustainable Railway Infrastructures project, completed between 2013 and 2016.


The research proposed is a noise and vibration measurement survey of existing standard and low-impact frog designs currently in use on North American transit systems. Ideally, the measurements would be completed at frogs at multiple transit agencies and at different stages in their life cycle. The measurement data would be used to accomplish the primary objectives of quantifying the noise and vibration reduction and determine the relative life-cycle costs provided by different low-impact frogs. The results would be presented in the form of guidance for selecting the appropriate low-impact frog for noise and vibration mitigation and for minimizing maintenance costs. A parallel information survey of transit agencies on what type of frogs they use and what their maintenance protocol and typical replacement rate is proposed to allow for an analysis of the expected life-cycle costs of frogs and an assessment of whether noise and vibration levels could be used as an indicator of when worn frogs should be repaired or replaced.

The tasks envisioned for the research are:

TASK 1 – Review of existing literature on low-impact frogs, including design, noise and vibration reduction, life-cycle costs, and implementation restrictions (such as speed restrictions).

TASK 2 – Survey of transit systems and track manufacturers on which types of frogs they use or manufacture, cost of the frogs, their typical replacement rate, and standard maintenance for frogs and wheels.

TASK 3 – Collect wayside noise and vibration data near frogs at several transit agencies. Transit agencies that have a variety of frog types in a variety of stages in their life cycle is preferred.

TASK 4 – Data analysis to determine the noise reduction provided by different frog designs and an assessment of whether noise and vibration levels are a useful indicator of when worn frogs should be repaired or replaced.

TASK 5 – Life-cycle cost analysis that looks at purchase, installation, and maintenance of different frog types. This task would also include identifying best-maintenance practices for extending the lifespan of the frogs and for keeping noise and vibration levels low.

TASK 6 – Document the findings in a final report. The report will include guidance for transit agencies on how to select an appropriate frog design for noise and vibration mitigation and guidance on best-maintenance practices for keeping noise and vibration levels low and extending the life-span of the frogs..


This research statement supports TCRP Strategic Priority III to continuously improve public transportation by enabling transit agencies to use the most effective frog designs for reducing noise and vibration levels, and will help identify best-maintenance practices for frogs that will maintain lower noise and vibration levels through the lifecycle of the frog. Other benefits of well-maintained, low noise and vibration frogs are higher speeds through special track-work, smoother rides, and lower costs.

Sponsoring Committee:AEP80, Transportation-Related Noise and Vibration
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Shannon McKenna
Source Info:This problem statement is the product of discussions with members of the TRB Committees AEP80 and ARO55 on urgent transit noise and vibration and track related research topics. The idea arose from discussions with track designers at transit agencies on the difficulty of implementing and maintaining moveable point frogs as a noise or vibration mitigation measure and separate discussions with track suppliers about the low adoption rate of some alternative low-impact frog designs, such as monoblock frogs, in North America. Individuals offering comment during development of this problem statement are:

Hugh Saurenman, ATS Consulting, Immediate Past Chair TRB AEP80
James T. Nelson, Wilson Ihrig
Briony Croft, SLR Consulting
Lawrence G. Lovejoy, WSP USA
Anthony Bahara, HDR Inc.
William B. Moorehead, TRAMMCO LLC

Others offering support to the problem statement are:
Shankar Rajaram, Sound Transit
Hugh Fuller, TY Lin, Chair TRB ARO55
Ruth Mazur, HNTB, Research Coordinator TRB AEP80
Date Posted:06/08/2020
Date Modified:06/15/2020
Index Terms:Frogs (Railroads), Railroad tracks, Noise control, Vibration, Vibration control, Noise, Flanges, Life cycle analysis,
Cosponsoring Committees: 
Public Transportation

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