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 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
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
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|
|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
|Index Terms:||Frogs (Railroads), Railroad tracks, Noise control, Vibration, Vibration control, Noise, Flanges, Life cycle analysis, |