601. Introduction - Inspection by foot, trollies, locomotives and rear vehicles enable the Permanent Way staff to carry out assessment of the quality of track. These inspections, though important, are qualitative and enable assessment based on individual experience. Objective assessment of track is done by track recording cars, Oscillograph cars and portable accelerometers.

602. Track Recording by Mechanical / Electronic Equipment - The following track recording equipments are in use in Indian Railways at present :-

(1) Track recording cars.

(2) Hallade track recorder.

(3) Oscillograph car.

(4) Portable accelerometers.

603. Track Recording Car - There are two types of track recording cars currently in use in Indian Railways, one mechanical and the other electronic. With these track recording cars, it is possible to have a continuous record of the track geometry under loaded conditions, by running the cars at nominated intervals.

604. Mechanical Track Recording Car (B.G.)- (1) It has two bogies one of two axles and the other of three axles. The measuring bogie has a base of 3.6 metres, and is three axled with an axle load of 7.0 tons. It gives a continuous record of -

(a) Unevenness - Left rail.

(b) unevenness - Right rail.

(c) Gauge.

(d) Twist.

(e) Curvature/alignment - Left rail.

(f) Curvature/alignment - Right rail.

(g) Speed

(2) The manner of recording of each parameter is indicated below :-

(a) Unevenness-The longitudinal unevenness of rails is measured as a deviation in the vertical plane (depression or rise) of the middle axle of the measuring bogie with reference to the average position of the two outer axles. The outer axles are spaced 3.6 metres apart and unevenness is recorded to scale of 1:1 on a base of 3.6 M. for left and right rail separately.

(b) Gauge -The changes in gauge are picked up by spring loaded gauge feelers which are in contact with the gauge faces at about 18 mm. below the rail table. The recording is done to a scale of 1:1. The feelers are so made that they can pass over the points and crossings and through check rails at level crossings without difficulty.

(c) Twist - Twist is measured as the relative out of planeness of one of the four wheels with respect to the plane formed by the other three wheels, of the outer axles of the measuring bogie. If, a, b, are the movements of the axle boxes of the leading axle and c, d, are the relative movements of the axle boxes of the rear axle then (a+d) - (b+c) gives the twist over a base of 3.6 M. The points from where these movements are picked up from the frame connected to the outer axles are so located as to compensate for the frame spacing being wider than the gauge. The twist is also recorded to full scale of 1:1.

(d) Curvature/Alignment - Curvature is deduced from the angle between the tangent and a chord of known length at any point of the rail, assumed to be circular. Two spring loaded feelers press against the rails from the tangents. The line joining the centres of the pivots of the two bogies forms the chord. By arrangement of cables attached to these feelers, the differential movement of the feelers with respect to the chord is transmitted to the recording table. The curvature is recorded as versines in mm. on a 7.2 M. chord. This measurement, however, is somewhat vitiated due to transverse play existing between the various parts of the vehicle such as between wheels and rails, between axles and bogie and between bogie and the vehicle. The magnitude of inaccuracy on this account is of a small order and the recording gives general guidance regarding the condition of alignment.

605. Electronic Track Recording Car - (1) Broad Gauge- (a) The construction features of this car are the same as those of the mechanical car excepting that the sensing elements of various track parameters transmit impulses electrically. Electrical track recorder gives out the various track parameters in analogue form on a graph paper.

(b) Details of the items of measurement -With the indigenously modified electronic track recording cars, it is possible to get a continuous record of alignment of each rail on a 7.2 M. chord in addition to the parameters described in Para 604 (1) above.

(c) Manner of Recording - In the electronic car, alignment is measured by versines on a chord length of 3.6 M. The mid-chord processor facilitates the conversion of the versines measured on 3.6 M base to 7.2 M base, electronically. This is according to

(2) Metre Gauge - (a) Construction features -The Metre Gauge track recording car is equipped with a measuring frame similar to the one provided in B.G. Track recording car. The transmission is electronic and the recording is done on a six channel B.N.L. recorder. The vertical and lateral acceleration are measured by an accelerometer fitted on the floor of the coach.

(b) Items of measurements- For Metre Gauge an indigenous track recording car is in use for recording the following parameters :

(i) Gauge.

(ii) Twist.

(iii) Unevenness - Left rail.

(iv) Unevenness - Right rail.

(v) Speed.

(c) (i) Gauge - The gauge is recorded at 14 mm. below the rail surface to a scale of 1:1. Feelers are pressed against the rail surfaces by spring loaded arrangement. The relative movements of the feelers are picked up by L.V.D. Ts. (Linear Variable Differential Transducer) and transferred to the recording table electrically.

(ii) Twist - It is recorded to a base of 2.74 metres, the distance between the two outer axles of a three axle bogie. The relative movements of the outer wheels with respect to carriage frames is picked up by L.V.D. Ts. In recording the twist some amplification is made to give appreciable record on the chart. A record of 5 mm. on chart is equivalent to 1 mm. / metre.

(iii) Unevenness is recorded over a base of 2.74 M. The relative movements of central axle with respect to the outer axles connected by a longitudinal beam is picked up with the help of suitable L.V.D. Ts.

606. Frequency of Track Recording - Track geometry monitoring of Metre Gauge routes is not to be done by track recording car. The Broad Gauge routes should be mointored by TRC as per the following frequencies (except for the routes where track recording is to be dispensd with):-

i) Routes with existing speeds above 130 kmph - Once in 2 months
ii) Routes with existing speeds above 110 kmph and upto 130 kmph. - Once in 3 months
iii) Other Group 'A' and 'B' routes - Once in 4 months
iv) Group 'C\ 'D' and 'D Spl.' routes - Once in 6 months
v) Group 'E' and 'E Spl.' routes - Once in 12 months

607. (1) Track categories for various Parameters - The track charts record - Imperfections in the form of peaks and the magnitude of the peaks is an indication of the extent of the defect. For each track parameter, track should be classified kilometre-wise based on the number of peaks and their magnitude occurring in that kilometre. The specified values for different categories for various parameters are given on next page - (Advance Correction Slip No. 96)

Note : (i) 10 points exceeding the outer limit of an irregularity under each category is allowed in 1 Km. length of track. If more than 10 peaks in one Km. cross the outer limits of 'A' category the kilometer is classified 'B' and so on. Based on the number of peaks and extent of irregularity the track is classified into 'A', 'B', 'C, and 'D' categories separately for each parameter-gauge twist, unevenness and alignment. 

(ii) The number of peaks in each kilometer exceeding the outer limit for the 'B' category is indicated as a suffix.

607(2) The following limits of track tolerances are prescribed for the guidance of the Engineering officials on the suitability of standard of maintenance of track for sanctioned speeds above 100 Km/hr. and upto 140 km/hr on BG track.

(i) Alignment defects - (versine measured on a chord of  7.5 metres under floating conditions)

a) On Straight Track - 5mm; values upto 10mm could be tolerated at few isolated locations**.

b) On Curves- 5mm over the average versine, Values up to 7mm could be tolerated at few isolated locations**.

Total change of versine from chord to chord should not exceed 10mm.

(ii) Cross Level Defects - No special tolerance limits. As regards cross levels, the track should be maintained, to standards generally superior to that at present available on main line track on which unrestricted speeds upto 100 Km/hr. are permitted.

(iii) Twist- (to be measured on a base of 3.5 m)

(a) On straight and curve track, other than on transitions - 2mm/metre except that at isolated locations**, this may go upto 3.5 mm /metre.

(b) On transitions of curves - Local defects should not exceed 1 mm/metres, except that at isolated locations** this may go upto 2.1 mm per metre.

(iv) Unevenness rail joint depressions (versine measured on a chord of 3.5m) - 10mm in general and 15mm for isolated locations**.

(v) Gauge variations - No special specifications. The maximum limits for tight and slack gauge should be as indicated in Para 224 (2) (e).

(*) Suitability - Suitability refers to good riding quality for passenger comfort and not from stability point of view.

(**) In above 'few isolated locations' has been taken as not exceeding 10 per km.

608. Analysis of track recording Car Charts- Prompt analysis of Track Recording Charts should be carried out in the track cell of Chief Engineer's Office. Analysis is done kilometre-wise for each parameter i.e., unevenness, twist, gauge and alignment and is classified into categories A, B, C and D for each parameter. The peaks on the points and crossings need not be counted in the number of peaks for categorisation. However, the quality of maintenance on points and crossings is judged solely on the basis of the peaks recorded. Statements are prepared, giving the results of the analysis of various parameters, P.W.I. - wise and A.E.N. - wise. Typical statements 1 to 9 as prepared for a Broad Gauge Section are enclosed as Statements 1 to 9. Similar statements are prepared for Metre Gauge sections with variations as necessary and the corresponding peak values adopted in categorisation.

Note : Figures in brackets Pertains to February, 1982 

I - Important %       D - Deterioration. % 

609.Arrangements for running track recording car - On receipt of track recording car programme from the R.D.S.O., the Zonal Railways should arrange for suitable power and path for the special along with telecommunication arrangement between the track recording car and the locomotive. The Headquarters should advise the Divisions concerned for making necessary arrangements to ensure that the Track Recording Car has an uninterrupted run.

610. Actual running of Track Recording Car - The Divisional Engineer, Assistant Engineer and Permanent Way Inspector of the section and nominated officer/staff of Headquarters office should accompany the Track Recording run. The Track Recording Car results vary appreciably with speed. The Divisional/Headquarters Officers accompanying the special should therefore ensure that the Track Recording Cars are run at the specified recording speed range of the particular car. The recording speed range of a Broad Gauge car is 70 km. p. h. - 80 km. p. h. and a Metre Gauge car 50 km. p. h. - 65 km. p. h. The recording done below these speeds are taken as "Non-recorded". For obtaining comparable results between successive recordings, it is necessary to run the special at uniform speed. The track recording car specials must run on through lines of ail stations. Recording should be done during day light hours. Before start of any run it should be ensured that the calibration of the car has been done satisfactorily. The charts should be taken out and sent to Headquarters Office for obtaining copies after the run - samples of charts obtained by (i) Broad Gauge Mechanical track recording car, (ii) Broad Gauge electronic track recording car, and (iii) Meter Gauge electronic track recording car are at Annexures 6/1, 6/2 and 6/3 respectively.

611. Action to be taken on Track Recording Charts - Spots (km.) requiring immediate attention, indicated by large peaks should be noted down by the Assistant Engineer/Permanent Way Inspector accompanying the car and immediate attention should be given to these kms. without loss of time. The charts should be analysed as detailed in Para 608 above and track classified into various categories as detailed in Para 607. A comparison of the records of each section with the previous run should be made and details of locations needing attention sent to the Division for onward transmission to maintenance units. Special attention should be paid by the maintenance units to the places where irregularities are high and where the defects are reappearing in successive recording runs.

612. Brief explanation of recordings - Explanation of the important parameters viz., twist, gauge, alignment and unevenness is given below -

(1.)Twist -When the recording car follows a straight path where both the rails are in one plane, the track of the twist line follows the datum line. On curves, however, the record will be as shown in sketch below (sketch 'A')

Sketch 'A'

The portions AB and CD indicate the transitions and BC the circular portion. For the circular portion the trace follows the datum line because there is no change of cross levels over the circular portion. The shift of the trace from the datum indicates the cant gradient.

A record as shown below will indicate the following defects (sketch 'B') :-

Sketch B'

(a) At the entry and exit of transitions there is sudden change indicating shock at entry and exit; smoothening is necessary.

(b) In the case of transitions, particularly AB, cant gradient is not uniform.

(c) Peaks in the circular portion indicate defective cross levels.

(2) Gauge - The trace indicates three conditions viz., correct gauge, tight gauge or slack gauge as shown-in Sketch 'C below -

Sketch 'C

The shift of the mean above the datum line indicates slack gauge as at BC. If the mean follows the datum, it indicates correct gauge as at AB. The shift of the mean below the datum line indicates tight gauge as at D. Uniform, tight or slack gauge is indicted by parallel shift of the track. In such cases gauge adjustment is not necessary provided the variation is within permissible limits. Isolated peaks indicate the necessity of spot-gauging.

(3) Alignment - The trace on a truly straight portion will follow the datum line as at AB in sketch 'D' below. On a curve the indication will be as at BCDE. The trace shows the versine diagram, BC and DE being the transitions.

Sketch 'D'

If isolated peaks are observed, local adjustment will serve the purpose. If the cant gradient over transition portion is non-uniform and there is wide variation of versines between adjacent chords, such curves call for realignment. By calculating the variation of versines over the mean line of the trace, cumulative frequency can be determined to decide the need for realigning.

(4) Unevenness- Unevenness is recorded by variation in the top level of each rail. It is normally noticed at joints either low or high. It is necessary to compare the records of both the rails. A peak on one of the rails only indicates twist which should be verified from the trace of the twist line.

The twist record should also be co-related to the cross-level record. Change in cross-levels over short length will indicate twist.

613. Monitoring of the riding quality of track- While the track recording cars can record the track geometry (i) the Hallade track recorders, (ii) the Oscillograph car, and (iii) the portable accelerometers record vertical and lateral accelerations, on which depends, the riding quality.

614. Hallade track recorder - (1) Generalise Hallade track recorder is an instrument which produces a graphic record of defects in alignment and surface of the track over which it is carried. The main parts of the instrument are -

(a) a drum rotated at a fixed speed by a clock work mechanism which carries a strip of paper 100 mm. wide covered over a carbon on which the chart is plotted,

(b) four sets of pendulums sensitive to movement in different directions which records the oscillations in those directions of the vehicle and track.

(2) Hallade Chart - Annexure 6/4 shows sample section of the Hallade chart. The top line, marked Line 1, is a record of the features of the route, on which telegraph posts, kilometre posts facing and trailing points in station yards, long bridges and tunnels are recorded by the Operator who makes the needle point producing this line move side-ways as the train passes any of the features, so making a small 'tick' in the line. A suitable convention for 'ticks' should be adopted to distinguish the physical features of the section.

Line 2 represents the alignment and is drawn after the test is carried out.

Line 3 represents the fore and aft "rolling" of the vehicle and registers sudden sags or humps and the acceleration of deceleration.

Line 4 represents lateral oscillations of the vehicle. Side to side motion of the vehicle causes the style to oscillate about the "medial line". The amount the style travels from the "medial line" is a comparative measure of the amount the vehicle diverges from its true path. Irregularities in alignment, uneven or incorrect superelevation on curves and uneven cross-levels are indicated.

Line 5 is a record of the vertical disturbance to the coach. Low or high joints, a bad top generally, or "hanging sleepers" are indicated.

(3) Frequency of testing with Hallade - On routes where Hallade track recorder is exclusively used for the track monitoring the following frequencies may be adopted :-

On B.G. On M.G. On N.G.
On C & D routes 6 months                                             On E routes Every year On Q routes 4 months                                      On R routes 6 months                                        On S routes Every year Every year

(4) Testing of track with Hallade -

(a) The Hallade track recorder should be placed on the leading bogie of the trailing vehicle or on the last but one vehicle, but the position of the vehicle must be the same in every run on a particular section.

(b) The Permanent Way Inspector should accompany the Hallade run.

(c) The same vehicle should be there every time preferably.

(d) Proper adjustment of the damping mechanism (critical damping) should be done.

(e) After completing the test, the chart should be completed in the following respects :-

(i) Heading the chart with particulars of date of test, train no., from station station ...................vehicle no., speed of the paper roll, and details of damping.

(ii) Checking up markings of kilometre posts, telegraph posts (electric masts) and filling in the speed of the train in km. p. h., km. by km.

(iii) Drawing line No. 2 indicating the right hand and left hand curve with the radius of each curve.

(iv) Drawing the medial line on line No. 4.

(v) Scrutinizing and marking track defects on the chart.

Blue prints of the chart should be then taken and 3 copies sent to the Assistant Engineer within a week of the test.

(5) Interpretation of the Charts - The charts are then analysed in the track cell of Chief Engineer's Office Kilometre-wise and the actual kilometres where alignment and packing defects have been recorded are listed out and given to the Assistant Engineer and Permanent Way Inspector for attention. The number of defects per km. are also worked out to enable the assessment of the track condition. The interpretation of the various types of typical defects noticed in a track are shown in Annexure 6/4. A typical analysis of an Hallade run in a P.W.I.'s/ A.E.N.'s section may be seen in the Statements 1 and 2, shown below.

(6) Attention to track defects recorded: -The Permanent Way Inspector should verify track defects indicated by chart at site, take expeditious action and report to the Assistant Engineer within a month.

On receipt of the Assistant Engineer's report the Divisional Engineer should get the chart examined with previous records and issue any orders he may consider necessary.

615. Oscillograph Car (1) Brief description of the car .-The main equipment in this car is an accelerometer, which consists essentially of a mass attached to one end of thin flexible plate, the other end of the plate being fixed firmly to the casing of the accelerometer. The space within the accelerometer casing is filled with a damping fluid (usually silicon liquid). The cantilever plate is strain gauged so that the deflection of the mass 'm' is sensed. This is calibrated to indicate the acceleration to which the mass is subjected. This acceleration is recorded in the form of an accelerogram. Thus the vertical and lateral acceleration on any part of the vehicle where the accelerometer is installed can be recorded. In track monitoring runs the accelerations at the loco cab floor are recorded by keeping the accelerometer as close to bogie pivot as possible.

(2) Details of recording : - the following parameters are recorded in the oscillograph car runs:-

(a) Vertical acceleration of loco cab.

(b) Lateral acceleration of loco cab.

In addition to the above, timing marks-one for every second-telegraph and km. marks and even marks such as station buildings, bridges etc., are also recorded on the chart. The primary spring deflections left and right are also recorded.

The chart obtained in an oscillograph car run can be seen at Annexure 6/5.

(3) Frequency of recording - These cars are used to monitor high speed routes where the sectional speed exceeds 100km./h. on B.G. and 75km./h. on M.G. These cars are run once in six months to assess the riding quality of the track as distinct from actual track geometry recorded by the Track Recording Cars. Recording is done at the maximum sanctioned speed of the section. On Rajdhani routes recording is done once in 4 months.

616. Analysis of oscillograms and interpretation of results -

(1) The Oscillograms obtained from the oscillograph car are analysed for the vertical and lateral acceleration.

(2) The analysis of records is done on the following lines :-

(a) All peaks are to be measured from the base or zero line i.e., no allowance is to be given when the trace shifts because of cant deficiency on curves. However, for the purpose of "ride index" calculations, lateral acceleration peaks are to be measured from the shifted base line on curves.

(b) The vertical and lateral accelerations above the threshold values are separately counted:

Threshold value of acceleration may be taken as follows :-

(i) In Loco Cab floor-The threshold value of acceleration in vertical mode is taken as 0.20 g. for all locos (Diesel and Eletric).

The threshold value of acceleration in lateral mode is taken as 0.20g. for diesel and electric locos with double stage suspension (i.e., for WDM-3, WDM-4, WDM-1, WDM-2/3 and WAG-2) with the exception of WDM-2 modified with single stage suspension.

In case of other locos, with single stage suspension (i.e.,WDM-2 std., WAM-1, WAM-4, WAG-1,WAG-3,WAG-4,WCG-2, WCAM, WCM, WCM-2, WCM-4 and WCM-5) the threshold value may be taken as 0.30g.

(ii) On Passenger Coach Floor .-The threshold value of acceleration for both vertical and lateral modes shall be taken as 0.15g.

(iii) The analysis is done kilometer-wise and results are given under the following heads, after counting the peaks above threshold value for the particular locomotive -

Station Yards,

Other than Station Yards(lsolated locations),

Active continuous stretches,

Speed grouping table is also prepared.

Typical Statement prepared in connection with an Oscillograph run are given below (Statement 'A' to 'C') -

Note - if there are on an average more than 10 peaks above the threshold value per Km. the length may be included in this statement.

617. Use of Oscillograph Car recordings :-

(1) Threshold values of acceleration are given in Para 616(2)/b. For ensuring good riding, track should be attended to at such locations where peaks above threshold values are noticed.

(2) Efforts should be made not only to check the extent of defect but also to find out whether it is occurring in an active patch; as such condition may lead to excessive oscillations.

618. Portable Accelerometers-

(1) General- OMS-2000 equipment's are portable accelerometers used for Oscillation monitoring using a portable accelerometer and transducers converting the oscillations to electrical signals which can be recorded electronically and processed on PC.

(2) Operation-The OMS Accelerometer is kept in the cabin of locomotive or on the coach floor, as close to the bogie pivot as possible. It is preferable that same coach and the same vehicular position are used in successive runs. The accelerations recorded are transferred to electronic recorder and are readable on the LCD display on real time basis. The stored data can be downloaded on TMS Computer for maintenance planning.

This equipment measures the Track Performance by measurement of vehicle response in terms of vertical and lateral accelerations. The real time output of the equipment is in the form of value of peaks exceeding the limiting value, their location and Ride Index. These values are available for both vertical and lateral accelerations.

(3) Frequency of Recording: 

(A) Broad Gauge :

Speed above 100 Km ph                                Once every month

Others                                                           Once in two months

(B) Meter Gauge : 

Speed above 75 Km ph                                  Once every month               

Others                                                          Once in two months

The above schedule is only a guideline. Chief Engineers may vary it, depending upon the availability of instrument and its use. For the time being A, B and C routes are to be covered once a month and other routes can be covered as per capacity and need.

(4) Recording of Defects: To assess the track quality, vertical and lateral acceleration peaks exceeding the values as below are to be considered:

Broad Gauge:

High Speed Routes above 110 Km ph On A & B routes                   greater than 0.15 g. 

Other Routes upto  110 Km ph                                                         greater than 0.2 g

Meter Gauge :                                                                                  greater than 0.2 g

(5) Classification of Track Quality - To classify a continuous section's (PWI's jurisdiction/sub-division/ division) track quality, the following criteria is to be used (average total number of peaks per km.):

  Very Good Good Average
High Speed                         Others Less than 1.0                            Less than 1.5 1 - 2                                          1.5-3.0 Greater than 2                        Greater than 3

The above criteria are for judging the quality of track. However, if the average number of peaks of vertical and lateral accelerations exceeding 0.30g is more than 0.25 per km or more than one in any particular kilometer, the track will need attention : At locations where peaks of lateral and vertical accelerations exceed 0.35g, the track will have to be attended to urgently.