53(a) Gage is measured between the heads
of the rails at right angles to the rails in a plane five-eighths of an inch
below the top of the rail head.
Guidance. See Figure 4 for an
illustration of gage measurements.
53(b) Gage must be within the limits
prescribed in the following table:
Guidance.
This rule establishes the minimum and maximum limits for gage on all tracks and
differentiates with the authorized speed, including a maximum gage dimension of
4 feet 10¼ inches for track in excepted status under §213.4.
Inspectors will make measurements at sufficient intervals to assure that
track is being maintained within the prescribed limits. Particular attention
should be given to track gage in turnouts or locations where high lateral train
forces are expected or evident. These areas include the curved closure rails,
the toe and heel of frogs, the curved track behind the frog and several feet
ahead of the switch points.
Where line or surface irregularities are observed by the Inspector, the gage
should be measured. Remember to look for evidence of lateral rail movement as
required in §213.13.
An accurate standard track gauge device or a rule graduated in inches is an
acceptable measuring device. Gage not within the specified limits of the TSS is
in non-compliance.
Alinement
may not deviate from uniformity more than the amount prescribed in the following
table:
Guidance.
This rule establishes the maximum alinement deviations allowed for tangent and
curved track in Classes 1 through 5 track.
Alinement (also spelled alignment) is the variation in curvature of each rail
of the track. On tangent track, the intended curvature is zero, and thus the
alinement is measured as the variation or deviation from zero. In a curve, the
alinement is measured as the variation or deviation from the "uniform"
alinement over a specified distance. The Inspector should note that the
procedures for determining uniformity in Classes 6 through 9 are similar to the
procedures described below. However, there are differences in the spacing of the
stations and the application of the chord measurements.
The point of greatest alinement deviation usually can be detected visually or
may be located by moving the chord along the track in increments until the point
with maximum deviation is found. In curves, the mid-ordinate, alternatively
called mid-chord offset (MCO), require "stations" to be marked at
regular intervals on the high rail in both directions from the point in
question. In tangent track, the MCO is measured directly with a 62-foot chord
and graduated ruler. In curves, a 62-foot chord is used in Classes 1 through 5
and a 31-foot chord is also used in Classes 3 through 5. The term MCO is used
interchangeably for "mid-ordinate" and "mid-offset" and
represents the distance from the rail to the chord at the mid-point of the
chord. For curves in Classes 3
through 5 track, an alinement defect may be in non-compliance with either the
maximum limits for the 31-foot chord or the 62-foot chord, or both. A 31-foot
chord is particularly necessary for determining short alinement deviations.
Inspectors must be aware that a 62-foot chord may be "blind" to short
alinement conditions, whereby a 31-foot chord can detect those non-complying
conditions. See Figure 5.
In Classes 3 through 5, both the 31-foot and 62-foot chords must be used,
and corresponding measurements must be calculated to determine compliance with
the required alinement thresholds. If alinement defects are found using both
the 31-foot and the 62-foot chord, the Inspector should report the item as one
defect and note that the defect does not comply with the requirements for the
second chord, e.g., "1¾ inches alinement deviation on curved track for
62-foot chord. Note: 1
⅜
inches alinement deviation for 31-foot
chord at this location."
The chord line (string) will be stretched and held taut between two points
on the rail,
⅝ inch
below the top running surface of the rail. Measure the MCO between the rail and
the string with a graduated ruler, using blocks to compensate for shallow
curvature and special trackwork, if necessary.
Since a true tangent has zero MCO, the measurement taken
can be compared directly to the alinement table under §213.55 to
determine compliance. On a curve of constant curvature or each arc of a compound
curve, mid-ordinates at all station points are equal when measured from chords
of equal length, exclusive of spirals. MCO’s, when measured from chords of
equal length, are nearly proportional to the degree of curvature.
Degree of curvature is the angle subtended at the center
of a simple curve by a 100 foot chord. Degree of curvature can be conveniently
measured using either a 31 or a 62-foot chord. Obtaining the degree of curvature
coupled with the average elevation in the area in question is necessary to
determine maximum authorized speed. Please refer to §213.57 for a
discussion on the determination of curvature.
Deviation of alinement on a curve requires determination
of the MCO over a specified number of stations and the average of those values.
The difference between the MCO at the
point of concern and the average must not
exceed the maximum deviation specified in the table in §213.55.
As shown in Table 5, an optional method to determine
average alinement includes 17 stations spaced at 15-feet 6 inches. For curves in
Classes 3 through 5, it is necessary to determine compliance with the
requirement for the maximum deviation of the MCO from a 31-foot chord in
addition to the 62-foot chord. Figure 6 illustrates the method to determine
alinement deviation using both chords.
When using the above procedures, the distance between the
first and last MCO will be 248 feet. However, note that in order to measure the
MCO at the first and last stations, the Inspector must place the end of the
string a station beyond the first and last one measured. As a reference, the
following table summarizes the acceptable proper chords, station spacing, and
number of stations to determine alinement compliance.
As previously indicated, the suspected alinement location
in a curve body is calculated by measuring an equal number of stations on each
side of the area in question. For the majority of occurrences, averaging the
MCOs on both sides of the location in question will develop sufficient data to
determine "uniform alinement." However, if the location in question is
close to or in a spiral, uniformity must be determined in a different manner. If
the location is located at the portion of a curve body close to a spiral,
measure the stations in the curve body only. That is, shift the averaging area
sufficiently so that none of the MCOs are in the spiral.
When measuring the body of a curve with a length that is
less than the distance spanned by the required number of stations, reduce the
numbers of stations accordingly. When measuring a compound curve, it will be
necessary to measure the MCOs within a sufficient portion of the entire curve to
determine where the curve bodies exist. Treat each curve body as a separate
curve and be governed by the above instructions.
Over the years, railroads have traditionally used a
31-foot chord to determine MCOs for higher degree curves. Although it is more
difficult to measure from the rail to the MCO at high degree curves, the
Inspector must determine alinement compliance in accordance with both the 62 and
31-foot chords described in this section.
In spirals, the alinement gradually changes from tangent
to the full degree of curvature at the curve body. Therefore, to determine an
alinement deviation at a given point in a spiral, it will be necessary to
determine the proper MCO based on the projected value at each point of concern.
The best method to determine the projected value at each point is to measure the
MCOs through the entire spiral in question. It is important to determine MCOs a
sufficient distance into the adjoining curve body and tangent track to
accurately determine the tangent to spiral (TS) and spiral to curve (SC). Place
the measured values in a graph and plot the spiral. The deviation at the point
of concern will be the difference between the MCO and the projected value. Use
the curve values from the alinement table to determine compliance in spirals.
Figure 7 shows a spiral calculation for 62-foot chord with
MCO units in 1/16
inch increments. A similar analysis is required for 31-foot chord for Classes 3
through 5. At station 5, the
existing value is 18 units (1⅛
inches) and the projected value is 12 units (¾ inch), therefore, the
deviation from uniformity is 6 units (⅜ inch).
57(a) The maximum crosslevel on the
outside rail of a curve may not be more than 8 inches on track Classes 1 and 2
and 7 inches on Classes 3 through 5. Except as provided in §213.63, the
outside rail of a curve may not be lower than the inside rail.
Guidance. Paragraph (a) does not
imply that more than 6 inches of superelevation is recommended in a curve;
rather the paragraph limits the amount of crosslevel in a curve to control the
unloading of the wheels on the high rail, especially at low speeds. The
crosslevel limits notwithstanding, this standard establishes the maximum
crosslevel at any point on the curve, which may not be more than 8 inches on
Classes 1 and 2 and 7 inches on Classes 3 through 5. In curves, crosslevel is
measured by subtracting the relative difference in height between the top
surface (tread) of the inside (low) rail from the tread of the outside (high)
rail. Both §213.63 and this section limit the amount of reverse
elevation (outside rail lower than the inside rail). While the table in §213.63
permits reverse elevation on a curve, the Vmax formula must also be checked
when reverse elevation is encountered. The Inspector must substitute a negative
number for the actual elevation in the formula as discussed below. The Vmax
formula applies only in the body of a curve.
57(b) (1) The maximum allowable operating
speed for each curve is determined by the following formula –
Vmax =
Where:
Vmax =
Maximum allowable operating speed (miles per hour).
Ea = Actual elevation of the outside rail
(inches)1.
D = Degree of curvature (degrees)2.
1Actual
elevation for each 15-foot track segment in the body of the curve is determined
by averaging the elevation for 10 points through the segment at 15.5-foot
spacing. If the curve length is less than 155-feet, average the points through
the full length of the body of the curve
2Degree
of curvature is determined by averaging the degree of curvature over the same
track segment as the elevation
Guidance.
Paragraph (b)(1) prescribes the formula to be used to determine the maximum
train speed in curves based on average curve alinement in degrees, and the
amount of superelevation at the same location. Several combinations of curvature
and elevation resulting in speed limitations may exist and should be considered
throughout the curve when determining compliance with this section.
A railroad car traveling around a curve is subjected to an outward horizontal
centrifugal force that acts conceptually through a car’s center of gravity
away from the center of the curve and tends to overturn the car by directing its
weight toward the outside rail. To counteract the centrifugal force, the outer
rail is elevated over the lower rail, or super elevated. In effect, the combined
effect of centrifugal force and weight produces a resultant force that is
intentionally moved toward the center of the track. A balanced (equilibrium)
condition implies the vertical forces on each rail are equal. Figure 8
illustrates the three types of balance conditions.
In practice, railroads generally do not
operate trains at balanced speed; that is, train speeds are set to move the
resultant force toward the outer rail, resulting in an unbalance typically less
than 3 inches. Unbalance or cant deficiency is the theoretical amount of
elevation that would have to be added to the existing elevation to achieve a
balanced condition. The TSS for Classes 1 through 5 limits the amount of
unbalance to 3 inches except that 4 inches is permitted for authorized and
approved equipment types. Waivers have been granted for operation at even higher
levels of cant deficiency.
Safe curving speeds are dependent on the
engineering characteristics of the specific equipment involved, as well as the
track conditions. Equipment factors such as center of gravity height, suspension
characteristics, reaction to wind and other factors are considered when FRA
makes a decision to approve a particular level of cant deficiency for specified
equipment.
The application of the Vmax formula uses an
averaging technique over a 155 foot "window." As indicated in sub-note
1, maximum train speed is based on values obtained from the curve body only. The
actual elevation and curvature to be used in the formula are determined by
averaging the elevation and curvature for 10 points, including the point of
concern for a total of 11, through the segment at 15.5-feet station spacing (31
and 62-foot chords). If a curve’s length is less than 155 feet, the
measurements are averaged over the full length of the curve. In order to
determine the average curvature, Inspectors must calculate the degree ofcurvature based on the chord length used
(either 31 or 62-foot) and the mid-chord offset measured at each station. For a
31-foot chord, the degree of curvature is determined by multiplying the
mid-chord offset by a factor of four (e.g., ¼ inch equals 1 degree). For a
62-foot chord, a one-to-one relationship exists (e.g., 1 inch equals 1 degree).
In addition to the limitations on reverse
elevation contained in the table in §213.63, the Vmax formula limits the
maximum authorized speed on a curve. Reverse elevation occurs when the inside
rail is higher than the outside rail; that is usually the unintended consequence
of track degradation. The condition can also occur where a turnout has been
installed in a main track (e.g., an equilateral turnout constructed in a
left-hand curve). Calculation of the maximum authorized speed for the curve with
negative elevation is performed in the same manner as one with positive
elevation. For example, the maximum authorized speed is approximately 13 m.p.h.
for a curve segment with an average curvature of 4 degrees and 2½ inches of
reverse elevation (both calculated over the 155 foot window or the length of the
curve), the calculation for 3 inches of unbalance would be as shown below:
57(b)(2) Table 1 of Appendix A
is a table of maximum allowable operating speed computed in accordance with
this formula for various elevations and degrees of curvature.
Guidance.
See Appendix A.
57(c)(1) For rolling stock
meeting the requirements specified in paragraph (d) of this section, the maximum
operating speed for each curve may be determined by the following formula –
Where:
Vmax =
Maximum allowable operating speed (miles per hour)
Ea = Actual elevation of the outside rail
(inches)1
D = Degree of curvature (degrees)2
Guidance. Paragraph (c)
permits approved types of equipment that have been qualified and approved by FRA
in accordance with paragraph (d), to operate at maximum allowable operating
speeds based on 4 inches of unbalance (cant deficiency). Inspectors must be
aware of those vehicles that have been approved by the Associate Administrator
for Safety for operation at 4 inches of unbalance.
57(c)(2) Table 2 of Appendix A
is a table of maximum allowable operating speed computed in accordance with
this formula for various elevations and degrees of curvature.
Guidance. See Appendix
A.
57(d) Qualified equipment may be
operated at curving speeds determined by the formula in paragraph (c) of this
section, provided each specific class of equipment is approved for operation by
the Federal Railroad Administration and the railroad demonstrates that:
(1) When positioned on a track
with a uniform four inch superelevation, the roll angle between the floor of the
equipment and the horizontal does not exceed 5.7 degrees; and
(2)
When positioned on a track with a uniform six inch superelevation, no wheel of
the equipment unloads to a value of 60 percent of its static value on perfectly
level track, and the roll angle between the floor of the equipment and the
horizontal does not exceed 8.6 degrees.
(3) The track owner shall notify
the Federal Railroad Administrator no less than 30 calendar days prior to the
proposed implementation of the higher curving speeds allowed under the formula
in paragraph (c) of this section. The notification shall be in writing and shall
contain, at a minimum, the following information --
(i) A complete description of the
class of equipment involved, including schematic diagrams of the suspension
systems and the location of the center of gravity above top of rail;
(ii) A complete description of the test
procedure3 and instrumentation used to qualify the
equipment and the maximum values for wheel unloading and roll angles which were
observed during testing;
(iii) Procedures or standards in
effect which relate to the maintenance of the suspension system for the
particular class of equipment; and
(iv) Identification of line
segment on which the higher curving speeds are proposed to be implemented.
3The
test procedure may be conducted in a test facility whereby all the wheels on one
side (right or left) of the equipment are alternately raised and lowered by four
and six inches and the vertical wheel loads under each wheel are measured and a
level is used to record the angle through which the floor of the equipment has
been rotated.
Guidance.
The engineering test described in paragraph (d) is known as the "static
lean test" which has been used by FRA for several years to evaluate a
vehicle’s curving performance.
For modern rail cars with a high center of
gravity (90 to 98 inches), low speed curve negotiation under excessive levels of
superelevation places the vehicle in an increased state of overbalance. This
condition creates the possibility of wheel unloading and subsequent wheel climb
when warp conditions are encountered within the curve, as explained by footnote
1 of the surface table in §213.63.
57(e) A track owner, or an operator of a
passenger or commuter service, who provides passenger or commuter service over
trackage of more than one track owner with the same class of equipment may
provide written notification to the Federal Railroad Administrator with the
written consent of the other affected track owners.
Guidance. Paragraph (e)
states that a track owner, or an operator of a passenger or commuter service
over trackage of more than one track owner with the same class of equipment, may
provide written notification to the FRA with the written consent of the other
track owner. Under paragraph (f) equipment presently operating at higher levels
of unbalance by reason of conditional waivers granted by FRA is considered to
have complied with the provisions of paragraph (d).
57(f) Equipment presently operating at curving
speeds allowed under the formula in paragraph (c) of this section, by reason of
conditional waivers granted by the Federal Railroad Administration, shall be
considered to have successfully complied with the requirements of paragraph (d)
of this section.
Guidance. Where FRA has approved higher
levels of unbalance, it becomes imperative that the Inspector monitor the
maximum authorized speeds
based on the approved unbalance. The calculation of the maximum authorized
speed for a particular segment of track involves the substitution of the
approved unbalance in the Vmax formula. This calculation is based on 10
stations, plus the point of concern, for a total of 11 stations spaced 15-feet 6
inches apart for a 62 or 31-foot chord. For example, if FRA approved 5 inches of
cant deficiency for a particular type of equipment, the maximum curving speed
for a 6 degree curve segment with 4½ inches of elevation would be calculated as
follows:
To determine an enforcement action, it is also necessary for the Inspector to
determine the actual unbalance based on the speed that the railroad is operating
around the curve and the actual track conditions. In order to calculate the
unbalance, the Inspector must solve the following formula, which is the same
Vmax formula represented in a different form:
Eu=Vmax2(0.0007)(D)-Eu
For example, if the railroad was operating around a curve at 100
m.p.h. and the Inspector determined, by field measurements, that the average
curvature and average elevation for a particular curve segment was 2 degrees and
5½ inches of elevation, respectively. The unbalance would be calculated as
follows:
Eu=(100)2(0.0007)(2)-5.5
Eu=(10,000)(0.0007)(2)-5.5
Eu=14-5.5=8.5"
Where FRA has not approved more than 3 inches of unbalance and
the operating speed on the curve produces more than 3 inches of unbalance, the
Inspector will record the circumstance as a defect. However, the Inspector
should consider writing a recommendation for civil penalty if the level of
unbalance based on the maximum speed, elevation, and curvature exceeds 4 inches.
When vehicle types have been approved by FRA for curving speeds producing more
than 3 inches unbalance, Inspectors will not consider recommending a violation
when operating speeds for that equipment only produce a marginal level of cant
deficiency above the approved level. The Regional Track Specialist should be
consulted when questions arise concerning limiting speeds in curves.
Figure 9 is an example showing the relationship between curvature, elevation,
and speed.
57(g) A track owner or a railroad
operating above Class 5 speeds, may request approval from the Federal Railroad
Administrator to operate specified equipment at a level of cant deficiency
greater than four inches in accordance with §213.329(c) and (d) on curves in
Class 1 through 5 track which are contiguous to the high speed track provided
that --
(1) The track owner or railroad submits a
test plan to the Federal Railroad Administrator for approval no less than thirty
calendar days prior to any proposed implementation of the higher curving speeds.
The test plan shall include an analysis and determination of carbody
acceleration safety limits for each rail car type which indicate wheel unloading
of 60 percent in a steady state condition and 80 percent in a transient (point
by point) condition. Accelerometers shall be laterally-oriented and
floor-mounted near the end of a representative rail car of each type;
(2) Upon FRA approval of a test plan, the
track owner or railroad conducts incrementally increasing train speed test runs
over the curves in the identified track segment(s) to demonstrate that wheel
unloading is within the limits prescribed in paragraph (g)(1) of this section;
(3) Upon FRA approval of a cant deficiency
level, the track owner or railroad inspects the curves in the identified track
segment with a Track Geometry Measurement System (TGMS) qualified in accordance
with §213.333 (b) through (g) at an inspection frequency of at least twice
annually with not less than 120 days interval between inspections; and
(4) The track owner or railroad operates
an instrumented car having dynamic response characteristics that are
representative of other equipment assigned to service or a portable device that
monitors on-board instrumentation on trains over the curves in the identified
track segment at the revenue speed profile at a frequency of at least once every
90 day period with not less than 30 days interval between inspections. The
instrumented car or the portable device shall monitor a laterally-oriented
accelerometer placed near the end of the rail car at the floor
level.
If the carbody lateral acceleration measurement exceeds the safety limits
prescribed in paragraph (g)(1), the railroad shall operate trains at curving
speeds in accordance with paragraph (b) or (c) of this section; and
(5) The track owner or railroad shall
maintain a copy of the most recent exception printouts for the inspections
required under paragraphs (g)(3) and (4) of this section.
Guidance. Paragraph (g) permits
a high-speed railroad (operating at Classes 6 through 9 speeds) with contiguous
(within or next to) curves Classes 1 through 5 to operate at a higher level of
unbalance on those curves provided that additional inspections and requirements
are maintained. Inspectors should compute allowable speeds through curves to
determine compliance with this section and report defects when train speed
exceeds the allowable based on the formula.
In most cases, the high-speed railroad will accomplish the testing
requirements for the Classes 1 through 5 curves during the qualification testing
under §§213.345 and 213.329 over the entire route which includes both low and
high-speed curves. In those cases, FRA approval will generally apply to all
curves on the route. However, FRA may approve different speeds or cant
deficiencies for different track segments, depending upon the results of the
testing.
59(a) If a curve is elevated, the full
elevation must be provided throughout the curve, unless physical conditions do
not permit. If elevation occurs in a curve, the actual minimum elevation must be
used in computing the maximum allowable operating speed for that curve under §213.57(b).
Section 213.59 is closely connected to §§213.57 and
213.63. When determining whether curved track is in compliance with the
TSS, Inspectors should consider §§213.57, 213.59, and 213.63 in
conjunction with one another. Because the language in §213.59 is
explanatory in nature and intertwined with the requirements in §§213.57 and
213.63, §213.59 should not stand alone in support of an alleged
violation. FRA Inspectors should cite either §213.57 or §213.63,
whichever is most applicable. Accordingly, FRA has not included any defect codes
for §213.59.
59(b) Elevation must be at a uniform rate,
within the limits of track surface deviation prescribed in §213.63 and
it must extend at least the full length of the spirals. If physical conditions
do not permit a spiral long enough to accommodate the minimum length of runoff,
part of the runoff may be on tangent track.
Items to consider with respect to runoff include the following:
• If elevation begins within the body of the curve rather than at the point
of curve-spiral, the least average elevation that exists in the body of the
curve will govern the allowable operating maximum speed throughout the full
curve.
• Elevation at the end of curves, or between segments of compound curves,
must be at a uniform rate within the limits of track surface deviations
prescribed in the table under §213.63.
• Particular attention must be given to the prescribed limits for
difference in crosslevel between any two points less than 62 feet apart on
spirals.
• If physical conditions do not permit a
spiral long enough to accommodate the minimum length of runoff, the runoff may
be carried into the tangent. In these circumstances, the surface table
parameters under §213.63 will govern.
• The actual minimum elevation and actual degree of curvature is determined
by using the averaging techniques described under §213.57.
Figure 10 illustrates how a railroad can reduce superelevation in the body of
the curve to accommodate a highway-rail grade crossing for unqualified equipment
(3 inches unbalance).
Each owner of the track to which this part
applies shall maintain the surface of its track within the limits prescribed in
the following table:
Guidance. Track
surface is the evenness or uniformity of track in short distances measured along
the tread of the rails. Under load, the track structure gradually deteriorates
due to dynamic and mechanical wear effects of passing trains. Improper drainage,
unstable roadbed, inadequate tamping, and deferred maintenance can create
surface irregularities. Track surface irregularities can lead to serious
consequences if ignored.
Allowable deviations in track surface include runoff at the end of a raise,
deviation from uniform profile, deviation from zero crosslevel at any point on
tangent or reverse crosslevel
elevation on curves, and the
difference in crosslevel between any two points less than 62 feet apart, are
specified in the track surface table. In addition, the table includes footnotes
that address three special circumstances.
The first parameter in the table in this section refers to the runnoff
(ramp) in any 31 foot segment at the end of a raise where the track is elevated
as a result of automatic or manual surfacing or bridge work. Conditions created
by track degradation (e.g., settlement or frost heaves) are to be addressed
using the uniform profile parameter, under this section. Trains encountering a
ramp (up or down) will experience a vertical pitch or bounce if the change in
elevation occurs in too short a distance. As in the more general profile
parameter, damage to car components, undesirable brake applications or
derailments may occur; especially when the vehicle experiences a lateral force
such as a buff force. Figure 11 illustrates the measurement of the runoff of
raised track.
The second parameter, profile, relates to the elevation of either rail along
the track. When trains encounter short dips or humps in the track it can result
in vertical separation of couplers, broken springs, bolsters, and truck frames.
Dips can result from mud spots, or develop at the ends of fixed structures
(e.g., bridges, highway rail grade and track crossings). Profile is determined
by placing the mid-point of a 62-foot chord at the point of maximum measurement,
irrespective of vertical curves. Profile may also be a track "hump"
cause by a frost heave or other occurrence. Figure 12 illustrates the
measurement of profile conditions.
Remember to consider any combination of rail and tie plate or
crosstie and ballast section voids to the mid-ordinate distance, according to §213.13
(dynamic loading). When
encountering a hump (e.g., frost heaves over culverts), place two uniform
(reference offset) blocks on top of the running rail. Stretch (taut) a 62 foot
string positioned over the blocks, with the observed highpoint at the midpoint
of the string. Measure the distance from the string to the running surface of
the rail. Subtract this distance from the height of the (offset) blocks to
determine the mid-offset.
The third parameter in the table refers to the deviation from
zero crosslevel at a point or reverse crosslevel in a curve. Crosslevel,
utilizing a levelboard, is measured by subtracting the difference in height
between the top surface (tread) of one rail to the tread of the opposite rail.
On tangent track both rails by design should be the same height, a term known as
zero crosslevel. On the spiral or body of a curve, the outer rail may not be
lower than inner rail (reverse elevation) beyond the limits provided in the
surface table. Also consider what implications, if any, Vmax (§213.57)
may impose at a curve body where reverse elevation is encountered.
The parameter for the difference in crosslevel between any two points less
than 62 feet apart is commonly referred to as the "warp" parameter.
This parameter provides maximum change in crosslevel between two points within
specific distances along the track. The warp parameter is, perhaps, the most
critical of the surface parameters. Excessive warp contributes to wheel climb
derailments. Figure 13 illustrates warp measurements.
The threshold values for warp represent minimum safety standards
that apply across the entire regulated industry and encompass the full range of
rolling stock in present day operating fleets. Inspectors should be aware that
some rolling stock, because of certain design and/or demonstrated performance
characteristics, may be subject to additional operating restrictions and/or more
restrictive warp thresholds as determined by individual railroads. The limits
for warp, applies anywhere along the track, (curves, spirals, and tangent
segments), except that the limits shown in footnote "*" of the §213.63
table (Table 6) apply in the special
case in spirals where physical conditions prevent the more restrictive limits in
the general warp parameter.
The footnote designated by a "*" of the §213.63 table
(Table 6) is an exception to the above warp requirement in spirals in those few
situations where the railroad has made a prior engineering decision, due to
physical restrictions, to design a shorter spiral that would be found in
standard construction. When encountering a spiral that does not have a
sufficient length to "runoff" elevation in accordance with the warp
parameter, the Inspector must determine if the "short spiral" is a
result of a man made or other natural obstruction. In short spirals, the amount
of warp is determined by measuring the "variation" in crosslevel
between two points 31-feet apart.
Examples of "short spiral" situations include rock cuts, tunnels,
station platforms, etc. Figure 14 illustrates the application of the
"*" footnote.
Railroads are expected to apply the
variation parameter and thresholds only at locations where there is a clear
history of restrictive physical characteristics.
When measuring track surface parameters remember the location of
the transition points between tangent, spiral, and curve body are determined by
actual physical layout and are not assumed to be synonymous with railroad
markers, tags, curve charts, or similar information. Therefore, be governed
accordingly when applying the "*" footnote or any other track geometry
parameter.
Under footnote 1 of the §213.63 table (Table 6), where the
Elevation At Any Point in a curve equals or exceeds 6 inches, the difference
(warp) in crosslevel within 62 feet between that point and a point with greater
elevation may not be more than 1½ inches regardless of track class. This
footnote is included to address the condition where a vehicle is operating on a
curve with a large amount of elevation and then encounters a warp condition.
Since the vehicle is typically in an unbalanced condition, the warp may induce
wheel climb. Slow speed curve negotiation is a particular concern since the
wheels on the outside rail of the curve will tend to unload due to the
overbalanced condition of the vehicle. Where this condition is found, the
appropriate corrective action would be reduction to Class 1 speed under the
provisions of §213.9(b).
Figure 15 illustrates a warp exceeding 1½ inches at a curve with 6 inches of
elevation.
Footnote 2 of the §213.63 table (Table 6) addresses the
critical harmonic rock-off condition that may result in the vehicle rocking back
and forth and derailing following wheel climb. It is considered rare that this
condition could occur in continuous welded rail (CWR), but it may occur where
"joint memory exists." In this case, while the condition is not a
defect unless it exceeds the warp limits specified in the table, the Inspector
should call the condition to the attention of the railroad. The crosslevel
difference (warp) may not exceed 1¼ inches on all six consecutive pairs of
joints, under the conventional joint spacing (33, 36, 39-foot long rails). Each
one of the six pairs must exceed 1¼ inches for this condition to be a defect.
Additional joints that have been introduced outside of the regular joint
spacing, characteristically as a result of rail repair, are not considered
harmonic "joints" for the purposes of this footnote. Figure 16
illustrates a harmonic rock-off condition.
A condition with consecutive low bolted joints may be in
non-compliance with either the warp limits specified in the table or the
requirements of footnote 2 of the §213.63 table (Table 6). Inspectors shall
consider any contiguous group of joints as one defect and note the number of
joints. If the harmonic condition continues beyond the seven joints, the
Inspector is not required to record another defect, but must note the number of
consecutive joints that make up the harmonic condition.
Jointed rail stagger that is not identical from stagger to
stagger, such as in a curve or when a rail slightly longer than the original
construction is installed, shall be considered in the harmonic calculation.
Additional joints introduced by the installation of short rails are ignored in
evaluating a harmonic condition.
Construction consisting of 79 or 80 foot rails does not result
in harmonic rock-off conditions since they occur outside of vehicle truck
spacing. For 79 or 80 foot rails and stagger spacing less than 10 feet, this
footnote is not applicable and Inspectors shall review the condition for
compliance with other track surface parameters.
Inspectors shall carefully apply the provisions of footnote 2 of the §213.63
table (Table 6). An acceptable remedial action is to raise and tamp one or two
joints in the middle of the consecutive low joints. This will break up the
harmonics.
