Subpart C – Track Geometry

Guidance. See the following figure for an illustration of gage measurements.

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 gage device or a rule graduated in inches is an acceptable measuring device. Gage not within the specified limits of the TSS is in noncompliance.

Alinement is the variation in curvature of each rail of the track. On tangent track, the intended curvature is zero; 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 noncompliance 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 noncomplying conditions. See the following figure.

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.

Di = the actual curvature at the ith point on the spiral, degrees

D = curvature of the curve, degrees,

Ls = spiral length, ft

The following figure represents a hypothetically case where the spiral length is 248 ft. (9 stations spaced at 31 ft). The chart would approximate a 1.44 degree curve whose curvature is gradually increased from 0 (at TS) to 1.44 degrees (at SC). The figure 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 measured 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 elevation of the outside rail of a curve may not be more than 8 inches on track Classes 1 and 2, and 7 inches on track Classes 3 through 5. The outside rail of a curve may not be lower than the inside rail by design, except when engineered to address specific track or operating conditions; the limits in §213.63 apply in all cases.

Guidance: The term "elevation of the outside rail" is relevant to the inside rail. In literature and in practice, it is also referred as superelevation. This paragraph does not imply that more than 6 inches of superelevation is recommended in a curve; rather the paragraph limits the amount of superelevation in a curve to control the unloading of the wheels on the outer rail, especially at low speeds. The limits establish the maximum superelevation 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, superelevation 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 this section and § 213.63 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.

The phrase "except when engineered to address specific track or operating conditions" is intended to address special cases, such as a turnout that comes off the high rail in a curve, to allow reverse elevation to be designed into the curve out of necessity and for safety reasons.

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 superelevated. 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. The following figure illustrates three scenarios for the given curvature and superelevation. The chart in the center indicates that if the vehicle is traveling at 42 m.ph., the equilibrium will be achieved. The chart on the left is an overbalanced scenario, in which a net inward acceleration (weight shifting to low rail) will result as the vehicle travels slower than 42 m.p.h. The chart on the right represents an underbalanced scenario, in which a net outward acceleration (weight shifting to high rail) will result as the vehicle travels fasters than 42 m.p.h. Using the vMax formula in this example, 3 inches of unbalance allows a maximum posted timetable speed of speed of 54 mph. Tolerance for localized degradation of up to 1 inch (Eu+1) results in a maximum speed of 57 mph. (§213.57(a) would apply to overbalance)

Guidance: This paragraph provides that all vehicle types are considered qualified for up to 3 inches of cant deficiency.

Guidance: The rule does not limit maximum level of cant deficiency in track Classes 1 through 5. However, the equipment must satisfy the requirements of this section. Consistent with the higher-speed standards in § 213.329, the requirements limit (1) vertical wheel load remaining on the raised wheels to no less than 60 percent of their static level values and (2) carbody roll for passenger cars to no more than 8.6 degrees with respect to the horizontal when the vehicle is standing (stationary) on track with a uniform superelevation equal to the proposed cant deficiency. The amount of superelevation will be the proposed cant deficiency. 

4 The test procedure may be conducted whereby all the wheels on one side (right or left) of the vehicle are raised to the proposed cant deficiency, the vertical wheel loads under each wheel are measured, and a level is used to record the angle through which the floor of the vehicle has been rotated.

Guidance: This paragraph clarifies the submittal requirements to FRA to obtain approval for the qualifying cant deficiency of a vehicle type. The load condition under which the testing is performed is required to be included in the description of the test procedure. The paragraph also includes the requirement for submitting suspension system maintenance information.

213.57(h)(1) Vehicle types permitted by FRA to operate at cant deficiencies, Eu, greater than 3 inches but not more than 5 inches shall be considered qualified under this section to operate at those permitted cant deficiencies for any track segment. The track owner or railroad shall notify FRA in writing no less than 30 calendar days prior to the proposed implementation of such curving speeds in accordance with paragraph (f) of this section.

(2) Vehicle types permitted by FRA to operate at cant deficiencies, Eu, greater than 5 inches shall be considered qualified under this section to operate at those permitted cant deficiencies only for the previously operated or identified track segments(s).

Guidance: This paragraph concerns vehicle types that have been previously permitted by FRA to operate at cant deficiencies, Eu, greater than 3 inches.

Paragraph (h)(1) states these vehicle types previously approved by FRA to operate at cant deficiencies, Eu, between 3 and 5 inches are considered qualified under this section to operate at the approved cant deficiencies on any track segment. The rationale to allow this portability is that the requirements of this section are steady-state and do not directly reflect the "local" vehicle and the track interaction.

However, the provision in paragraph (h)(2) restricts the "portability" of cant deficiency qualification for vehicle types that have been permitted by FRA to operate at cant deficiencies, Eu, greater than 5 inches. Operation at cant deficiencies greater than 5 inches over other track segments must be newly qualified in accordance with this rule, consistent with the additional requirements for the safety of operations at cant deficiencies greater than 5 inches.

213.57(i) For vehicle types intended to operate at any curving speed producing more than 5 inches of cant deficiency, the following provisions of subpart G of this part shall apply: §§213.333(a) through (g), (j)(1), (k) and (m), 213.345, and 213.369(f).

Guidance: The paragraph applies to operations at cant deficiencies greater than 5 inches. The requirements for operations of more than 5 inches cant deficiency apply to all classes of track. These requirements are specified in §§ 213.333, Automated vehicle-based inspection systems, paragraphs (a) through (g), (j)(1), (k) and (m); 213.345, Vehicle/track system qualification; and 213.369, Inspection records, paragraph (f). These requirements are briefly summarized below. For complete guidance on § 213.333 and other provisions of subpart G please see Volume II, Chapter 2 of this manual.

(j) As used in this section—

(1) Vehicle means a locomotive, as defined in §229.5 of this chapter; a freight car, as defined in §215.5 of this chapter; a passenger car, as defined in §238.5 of this chapter; and any rail rolling equipment used in a train with either a freight car or a passenger car.

(2) Vehicle type means like vehicles with variations in their physical properties, such as suspension, mass, interior arrangements, and dimensions that do not result in significant changes to their dynamic characteristics.

Guidance: Paragraph (j) clarifies "vehicle" and "vehicle type." The paragraph is of particular importance when determining if a vehicle type is subject to the qualification requirements of this section. For example, a vehicle type with modified primary springs to improve performance at different speeds may be considered a new vehicle type and hence subject to the qualification requirements of this section.

Guidance: Items to consider with respect to runoff include the following:

• 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.

213.63(a) Except as provided in paragraph (b) of this section, each track owner 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.

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). A profile is determined by placing the mid-point of a 62-foot chord at the point of maximum measurement, irrespective of vertical curves. A profile may also be a track "hump" caused by a frost heave or other occurrence. The following figure illustrates the measurement of profile conditions.

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 threshold values for warp represent minimum safety standards 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 apply anywhere along the track, (curves, spirals, and tangent segments), except that the limits shown in footnote "*" of the table 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 table 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. The following figure 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 table, where the elevation at any point in a curve equals or exceeds 6 inches, the difference in crosslevel (warp) 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).

The following figure illustrates a warp exceeding 1½ inches at a curve with 6 inches of elevation.

213.63(b) For operations at a qualified cant deficiency, Eu, of more than 5 inches, each track owner shall maintain the surface of the curve within the limits prescribed in the following table: