Permanent Way

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Track Classifications

Q. What is an ‘A’ class line, or a ‘Q’ class line, etc.?

The permanent way sections are classified by IR according to the maximum speed (or more precisely, the maximum speed proposed for the immediate future) that the tracks are capable of supporting. In most cases this classification is more an indication of the priority of the route and IR's plans for it in the future, rather than an indication of the speeds allowed on it today. Also, some small stretches of a line may have much higher (or lower) allowed speeds than the classification of the line might indicate because of local conditions, mountainous terrain, sharp curves, etc.

A class: Lines in these sections are BG sections rated for speeds unto 160km/h. These are:

  • New Delhi - Howrah (via the Grand Chord and Howrah - Barddhaman Chord)
  • New Delhi - Mumbai Central
  • New Delhi - Chennai Central
  • Howrah - Nagpur - Mumbai CSMT

(09/2020) Even though these are classified as A class, only the first two are being actively upgraded to support 160km/h operations, the rest will be limited to 130km/h.

In 2004, there were mentions of the Ratnagiri - Sawantwadi section of KR being included in the A class, but no confirmation of this was found. The latest edition of the IR Permanent Way Manual (June 2020) does not make a mention of this section.

Apart from the standard 'A' class lines mentioned above, IR through its subsidiary company, NHSRCL (National High Speed Rail Corporation Limited) is constructing a high-speed line between Mumbai and Ahmedabad to support Shinkansen-like services capable of speeds of upto 320km/h. The NHSRCL also plans to construct high-speed lines in other parts of the country, notably between Bangalore - Chennai and Mumbai - Nagpur.

B Class: This class allows speeds up to 130km/h. The following sections are mentioned in the IR Permanent Way Manual (July 2019):

  • Pathankot - Ludhiana - Ambala - Saharanpur - Lucknow - Mughalsarai - Patna - Kiul - Barharwa
  • Ambala - Kalka
  • Ghaziabad - Saharanpur
  • Khana - Barharwa - Malda Town - Jalpaiguri
  • Kharagpur - Vishakhapatnam - Vijayawada
  • Vadodara - Ahmedabad
  • Bhusawal - Itarsi - Jabalpur - Prayagraj (Allahabad)
  • Kalyan - Pune - Wadi - Guntakal - Renigunta - Chennai Central
  • Gooty - Dharmavaram - Bengaluru
  • Bengaluru - Jolarpettai - Chennai Central
  • Chennai Central - Salem - Coimbatore - Ernakulam
  • Chennai Egmore - Dindigul

C Class: This is not really a speed-rated class, but is the classification used for suburban sections of metropolitan areas.

D Special Class: This class is for lines that have an annual traffic density of 20 GMT or more. Speeds allowed are a maximum of 110km/h. These lines cover many sections in Central India where mining and related industries are common. Lines in this class also include many feeder and branch lines that connect to those in the A and B class. An exhaustive list of these lines can be found here.

D Class: This class is essentially same as above, except that the annual traffic density is lower than 20 GMT. Maximum speeds remain at 110km/h.

E Class: For all other branch lines and sections that are not classified as above. Speeds in this class are a maximum of 100km/h.

Previously, there was an E special class which classified routes that had potential for higher traffic growth with speeds limited to less than 100km/h. The last few editions of the Permanent Way Manual have done away with this class and merged these lines with either D or D special.

Q class: These were MG lines rated for speeds above 75km/h and traffic generally above 2.5 GMT. Some (such as Delhi - Jaipur) allowed speeds up to 105km/h or so (Pink City Exp., etc.) and had concrete sleepers and welded rails. In 1999/2000, when the list was last revised, the following sections were classified Q:

  • Rewari - Ringus - Phulera
  • Ratangarh - Degana
  • Delhi Sarai Rohilla - Rewari - Ratangarh
  • Ajmer - Ratlam - Khandwa
  • Jaipur - Phulera - Ajmer
  • Bandikui - Agra Fort
  • Ahmedabad - Bhavnagar
  • Agra - Mathura - Bhojipura - Lalkuan
  • Bhojipura - Lucknow Jn
  • Villupuram - Thanjavur - Thiruchirapalli
  • Chennai Beach - Villupuram (added in 2000)
  • Dindigul - Madurai (added in 2000)

In addition to the above, these MG sections were in the 'Q' class in 1985 (incomplete list):

  • Ratangarh - Rewari
  • Jodhpur - Jaipur - Agra East Bank
  • Kathgodam - Bhojipur
  • Bangalore - Hubli - Miraj

R class: These were MG lines rated at up to 75km/h. This category was further broken down into three classes based on traffic density: R-1, R-2, and R-3 (in decreasing order of traffic carried).

  • R-1 routes (traffic above 5 GMT/year): As of 1985, this included Hospet - Hubli, Secunderabad - Guntakal, Londa - Marmagoa, Katihar - New Bongaigaon, Guwahati - Tinsukia, and Gandhidham - Palanpur. Only Gandhidham - Palanpur remained in this category by 1999.
  • R-2 routes (traffic of 2.5-5.0 GMT/year): As of 1985, this included Guntakal - Hospet, Guntakal - Villupuram, Tiruchirapalli - Manamadurai - Virudunagar, Purna - Secunderabad, and Jodhpur - Marwar. By 1999, the list consisted of just Secunderabad - Mudkhed, Guntakal - Bellary, Guntakal - Villupuram, Thiruchirapalli - Manamadurai - Virudunagar.
  • R-3 routes (traffic of 1.5-2.5 GMT/year): As of 1985, this included Madurai - Rameswaram, Virudhunagar - Tenkasi, Dindigul - Pollachi, Ratangarh - Bikaner - Merta Rd., Muzaffarpur - Narkatiyaganj, and Birur - Shimoga Town. By 1999, the list consisted of Madurai - Rameswaram, Virudunagar - Tenkasi, Dindigul - Pollachi, and Ratangarh - Bikaner.

S class: These were all the remaining MG lines rated for below 75km/h and/or with low traffic densities (below 1.5 GMT/year).

There are no classifications like the above for narrow gauge tracks.

(03/2021) With only a handful of MG lines remaining in operation, it is not known what their current classifications are. Latest lists and manuals omit these lines completely.

As mentioned above, these speeds are the maximum that the tracks are built to support. Actual running speeds are usually much lower because of other considerations (traffic on the line, signalling arrangements, curves, proximity to populated areas, presence of points and divergences/convergences, etc.). Based on this the maximum permissible speed is specified for each section of a route.

Normally only the main line can be traversed at that speed. Turnouts to diverging routes require a reduction in speed. Most turnouts have speed restrictions of 30km/h (1 in 12 or easier). In the case of turn outs 1 in 12 turnouts (or easier) laid on concrete sleepers with thick web switches, speeds are marginally higher at 50km/h.

Sharp turnouts (1 in 8, NG turnouts of 1 in 8.5, etc.) are limited to 15km/h or even 10km/h or 5km/h in some cases. (A few NG lines have even sharper turnouts; e.g., the DHR has a 1 in 5 turnout and 1:4 crossings. Speeds are restricted appropriately in such cases.) In practice many of these are crossed at higher speeds depending on local conditions and the driver's knowledge of the track.

RDSO Proposed BG Turnout Speed Restrictions
Turnout Speed Restriction
1:8.5 turnout with straight switch 10 km/h
1:8.5 turnout with curved switch 25 km/h
1:12 turnout with straight switch 15 km/h
1:12 turnout with conventional curved switch (0°27'35" switch entry angle) 40 km/h
1:12 turnout with improved curved switch 50 km/h
1:12 turnout with thick web switch 50 km/h
1:16 turnout with symmetrical split curved switch 75 km/h
1:16 turnout with conventional curved switch 50 km/h
1:16 turnout with high speed curved switch 60 km/h

Note that some railbuses and other vehicles are allowed a higher speed than normal on sharp turnouts because of their smaller wheels. The presence of curves, insufficient cant, etc. can further require reductions in allowed speed.

Several high traffic junctions (like Wardha on the Nagpur - Mumbai line) have had their layouts modified to feature easier curves and high-speed turnouts featuring modified thick web switches. These allow for speeds of upto 85km/h during traversal though they are restricted to 60 km/h in regular operations. These modified high-speed switches are being installed across the network in a phased manner.

Traffic based classification

Some older documents and other sources of IR make reference to a purely traffic-based classification system for tracks. This system is no longer in use.

In this, lines were classified as: 'HM' or Heavy Mineral - BG mineral and ore freight lines; 'A' - BG lines with more than 3 million gross tonnes or MG lines with more than 2 million gross tonnes of traffic; 'B' - BG lines with 0.75 to 3 million gross tonnes or MG lines with 0.5 to 2 million gross tonnes; 'C' - BG lines with 0.5 to 0.75 million gross tonnes of traffic, or in some cases, defined as any lines carrying 3 or fewer trains a day; and 'D' - light lines with no or little existing traffic built for passenger services or for the purpose of stimulating commercial activity in underdeveloped areas.

Specifications and Track Construction

Q. What are the dimensions of IR track formations?

Please consult the diagrams available on the following pages:

  • Track Formation Diagram: This page shows a cross-section of a typical track formation showing the different components that make it up and the usual terms associated with them.
  • Track Dimensions Diagrams: This page shows dimensions for common types of tracks (MG and BG), both single line and double lines, on embankments and in cuttings.

Q. What weights and kinds of rails does IR use?

Broad Gauge

The IRS standard for mainline tracks (both new construction and renewals) is 60kg/m (really 60.34kg/m, 130.4lb/yd). 52kg/m (really 51.89kg/m, 105lb/yd) rail is also used extensively, but as renewals take place, these are being replaced with newer 60kg/m rails. Smaller sidings, loop lines and private branches will retain 52kg/m rails. Both allow for 25-ton axle loads. A 62kg/m standard has also been mooted, but status is unknown as of now (03/2021).

Until about 1970, most sections had RBS standard rails of 44.7kg/m (90lb/yd). The RBS standard had been adopted in 1914, and allowed 22.5-ton axle loads at 100km/h. BG branch lines in the past used 37.2kg/m (75lb/yd), 42.2kg/m (85lb/yd), and 44.7kg/m (90lb/yd) rails.

Broad Gauge Routes and Rail Weights
Traffic Density in GMT/yr Track Classification
A B C D Spl D E
> 20 60kg 60kg 60kg 60kg 60kg 60kg
10-20 60kg 60kg 60kg 60kg 60kg 52kg 90UTS
5-10 60kg 52kg 90UTS 52kg 90UTS 52kg 90UTS 52kg 90UTS 52kg 90UTS
< 5 52kg 90UTS 52kg 90UTS 52kg 90UTS 52kg 90UTS
or 60kg SH
52kg 90UTS
or 60kg SH
52kg 90UTS
or 60kg SH
Loop Lines 52kg SH 52kg SH 52kg SH 52kg SH 52kg SH 52kg SH
'SH' = Second-hand

The 60kg/m rails (and the 52kg/m ones) mentioned above are made of a steel of strength 90ksi ultimate tensile strength (90UTS steel). Some sections with heavy mineral freight traffic use steel rails of 110UTS. The move to 90UTS steel was necessitated because of the heavier loads and also to minimize wear from the harder steel used for the cast wheels manufactured by the Wheel and Axle Plant (now Rail Wheel Factory) especially for the newer BOXN wagons.

The steel used is a medium manganese type with some chromium and vanadium as well. Rails are often head-hardened (heat treated to harden the top surface) as well ('HH' rails).

About 95% of the 60kg rails are used for track renewals, track doubling, or gauge conversion, only about 15% of all rail production being needed for single-length rail repair, points, and crossings. For 52kg rails that figure is around 85%. 60kg/90UTS medium manganese rails have a service life of 800GMT, specified in terms of a traffic limit. The corresponding figure for 52kg rails is 525GMT. Head hardening of the rails increases the service life considerably, often by a factor of 2 or 3.

The older rails (until about 1993) of 90lb/yd, etc., were of 72UTS medium manganese steel which were suitable for use with the older forged wheels. The 90UTS steel now used routinely, and especially the 110UTS steel used in some places, require extra care in the production of the rails as well in their transport and maintenance since they tend to be less resistant to brittle fracture on encountering bending or impact stresses.

The metallurgical quality of the steel was of some concern especially after a derailment at Khanna in Punjab in 1999 was blamed on rails snapping due to excessive hydrogen left behind in the rails during manufacture. The older 72UTS steel rails expanded up to about 14% under thermal and mechanical stresses, whereas the 90UTS and higher tensile strength rails expand much less (10% for 90UTS). This allows the 90UTS rails to be welded together for longer lengths with the provision of expansion joints less frequently than for the 72UTS rails.

The Steel Authority of India Ltd. (SAIL) is the main supplier of all kinds of rails for IR, although some initial consignments of 110UTS steel rails were also imported in the mid-1990s. (See below for suppliers.)

Rail Dimensions and Other Specifications

Cross-sectional area for BG rails ranges from 7686mm2 for 60kg UIC rails to 6615mm2 for 52kg IRS rails. Rail height is 156mm for 52kg rails, and 172mm for 60kg rails. Flange width is 136mm (52kg rails). The 90UTS rails have a hardness of 260BHN, while the 72UTS rails have a hardness of 230BHN.

Chemical Composition

90UTS Rails: Manganese: 0.8-1.3%. Silicon: 0.1-0.5%. Sulphur(sulfur): 0.03% max in 880 grade rails. Carbon: 0.6-0.8% in 880 grade rails. Phosphorus: 0.03% max in 880 rails.

72UTS rails (historical): Manganese: 0.95%-1.4%. Silicon: 0.05% to 0.30%. Sulphur (sulfur): 0.035% max. in HH rails, 0.04%-0.05% in 710 grade rails. Carbon: 0.72%-0.82% in HH rails, 0.45-0.6% in 710 grade rails, 0.6%-0.8% in 880 grade rails. Phosphorus: 0.035% max. in HH rails, 0.05% max. in 710/880 grade rails.

Metre Gauge

Starting in the late 80s track renewals on MG were carried out using 52kg rails, but these were not widespread. Busier MG sections were laid (or renewed) using 37.2 kg/m rails. This was an IRS standard adopted in the early 1970s and allowed 17.5-ton axle load.

However, much of the MG trackage still used the older RBS standard adopted in 1914, which specifies 27.6kg/m (60lb/yd) (allowing 13-ton axle loads and 75km/h speeds).

(03/2021) At present it is not known which rail weights the remaining MG lines use.

Narrow Gauge

There was a large variety of rails used for NG lines. Common rail weights were 14.9kg/m (30lb/yd), 19.8kg/m (40lb/yd), 20.5kg/m (41.3lb/yd), 24.8kg/m (50lb/yd), and 37.2kg/m (75lb/yd) (this last kind was essentially the same rails for MG being re-used on NG sections). The Darjeeling Himalayan Railway originally had 30lb or lighter rail, which was replaced quite early on with 41-1/4lb rail. After Independence much of it was replaced with 50lb rails and in more recent times, much relaying has been done with 60lb rails obtained from MG gauge conversions. Most NG lines have flat-bottomed rails, although a few had bull-headed rails.


GIPR's first BG tracks used 65lb/yd double-headed rails made of wrought iron. Rails of 80lb/yd were common (e.g., Indian Midland Railway). Both flat-bottomed and bull-headed rails were commonly used. MG railways started off with 40lb/yd rails, although 30lb/yd rails were also used. The Barsi Light Rly. used 30lb/yd rails. The Rajputana Malwa Rly. used 50lb rails.

Q. What are the common lengths of rails?

The most common length for BG rails are 13m (42'8") and 26m (85'4").

MG rails were usually 12m (39'4") in length. NG rails vary, but the commonest length is 9m (29'6''). Much earlier (before the metric system was adopted!), rails were generally produced in sizes of 11, 12, or 14 yards (33', 36', 42'), less commonly 13 yards (39') or 10 yards (30' - NG).

Welded rail sections are of two types: Short Welded Rail or SWR which consists of just two or three rails welded together, and Long Welded Rail or LWR which covers anything longer. (In the past, there was a distinction made between LWR and Continuously Welded Rail, or CWR, based on the length — in CWR, the total length was 0.75km or more. The term 'CWR' is no longer used although you may still find it in old documents or painted signs.)

LWR is typically any length larger than twice the breathing length, which is the length allowed at the end of the welded rail section which is free to expand or contract as the temperature changes. (Beyond the breathing length, the rails do not move because of the resistance of the fasteners and the sleepers and ballast.) The breathing length varies with the temperature range, the sleepers, and the type of rails, but is typically 10m or less with concrete or steel sleepers. The expansion range of the rails is reduced with the steels of higher tensile strength, such as the 90UTS and 110UTS steels, allowing longer welded sections to be built.

With welded sections, the maintenance and safety problems of having rail joints with fishplates, etc., are reduced, but welded rail also calls for more precise provisioning of de-stressing/pretensioning to account for thermal expansion, etc. SWR with three-rail welded panels results in 28-30 fish-plated joints over the distance of a kilometre, which is the source of the commonly heard (and beloved of railfans) clackety-clack rhythm of the wheels.

LWR is usually formed from panels of 10-rail or 20-rail length welded using flash butt welding at manufacturing plants or specialized IR shops (Meerut, Gonda, etc.). The welded rails are transported on special rail flat wagons which have end unloading chutes. LWR and CWR are also formed by in situ welding of the rails using alumino-thermic welding (also known as thermite (thermit) welding). In this, the highly exothermic reaction of aluminium with ferric oxide (provided as a paste called thermite)results in temperatures of around 2500C and the reduction of the ferric oxide to elemental molten iron that then helps form a weld. More details on thermit welding here. Also see the item below on welding.

Bhilai Steel Plant makes 80m rails as its basic design at the plant and the Jindal Steel Plant makes 121m rails; however, usually these are cut to form the 13m and 26m rails to allow proper degassing and controlled cooling.

Initially, only 13m rails could be produced — Bhilai Steel Plant was unable to make rails to the right specifications at longer lengths, and IR also did not have facilities for transporting longer rails. An experiment in the mid-1990s to produce 26m rails was unsuccessful. However, more recently, rail production technology has improved, and longer rails can be produced by Bhilai Steel Plant with the requisite low levels of hydrogen gas and conformance to other specifications.

In 2003, the Bhilai Steel Plant started trial production of extra-long pre-welded rail panels (260m long, which is 10x the length of normal rails, and also 240m panels — this is a convenient multiple of the 80m manufactured length of rails from the plant). Serial production and supply of 260m rails started in February 2009. As of October 2020, Jindal Power and Steel also supplies 260m long rail panels.

Q. What are ‘thick web switches’ (‘thick webbed switches’)?

The term thick web switches most commonly refers to a 2002 design of sturdier BG switches on prestressed concrete sleepers, which can handle higher turnout speeds. These are made for 1:8.5 turnouts (less commonly, 1:12), with 160mm (less commonly 115mm) throw, and have clamp locks, spring setting devices (SSD), and the ZU-1-160 thick web rail. In 2003 or 2004, IR decided to use these switches on all the Class A routes and other high-density routes with traffic above 20GMT/year. The new switches have been designed to be easily installable on top of existing prestressed concrete sleepers supporting older switches.

Q. What types of welding are used for rails?

Principally two types of welding are used for rails. One is Flash Butt Welding, and the other is Alumino-Thermic Welding, also known as Thermit(e) welding. A third kind of welding, known as Gas Pressure welding, is used much less often, and a fourth kind, Metal Arc Welding, is very rarely used.

Flash Butt Welding

In Flash Butt Welding, a strong electric current is passed through the metal body of the rail in the vicinity of the spot which is to be welded, and the resistance of the rail to the current results in localized heating which melts the metal. No additional material is added, and the parent metal of the rails itself forms the material of the weld. About 25mm to 35mm of the rail length is consumed in the melting process.

Flash butt welding is done in mostly automated way using a machine that clamps and firmly holds together the two ends of the rails to be welded. When the two end surfaces are close together and the electricity turned on, the current arcs over or 'flashes' at the junction between the rail ends. The rail ends are moved back and forth to keep the flashing going and generate enough heat to melt the metal at the ends. The flashing cycles are adjusted so that the current flows without creating a short-circuit situation nor leaving it at an open circuit for too long. Typically, the weld current reaches 30,000 to 80,000 amps at about 400V to 500V. The machine then forces the ends of the rails together with high pressure after the metal at the ends has melted, to consolidate the joint as it cools and solidifies. Pressures range from 5kg/mm2 for 72UTS rails to 6kg/mm2 for 90UTS rails and 7kg/mm2 for 110UTS rails.

When the weld has set, an operation of stripping is carried out to remove excess metal that has solidified around the joint. Then the rail is cooled and straightened out. As with all welds, the joint has to be ground smooth so the weld surface is flush with the parent rail surfaces. Variations in the techniques include methods for initial burn-off and preheating, flashing cycle variations, methods of cooling, etc.

Alumino-Thermic Welding

In Thermit Welding or Alumino-Thermic Welding, the two ends of the rails are not brought into contact; instead, the gap between them is filled with molten material created by the exothermic reaction of aluminium and iron oxides. More details on thermit welding can be found here. Thermit welding is a manual process requiring considerable skill on the part of the welders. Traditionally, IR used conventional thermit welding, but in recent years has switched almost completely to the Quick Thermit Welding process, also known as the 'short pre-heat' or 'SKV' process. This saves time in the welding process but puts a higher premium on the welders' skills.

Flash butt welding is generally considered to be superior to thermit welding because it is essentially a forging process and the material of the weld is chemically identical to the parent body of the rails, which means its strength and other characteristics are almost identical to those of the body of the rails. Flash butt welding also typically results in fewer defects such as contaminant particles, porosity, etc., at the weld. Thermit welding also requires a higher quality of rails as a precondition -- rails that are corroded, twisted or warped, hogged or battered, or excessively worn cannot be welded by the thermit process as faults can propagate into the weld material and cause weld fractures.

Other Methods

Gas Pressure Welding is a solid phase welding technique. Oxy-acetyline flames are used to heat the ends of the rails to be welded to 1200°-1300°C, and they are then placed in contact with one another at high pressures, leading to the formation of a solid bond. ER had one gas pressure welding machine from Japan that was imported in 1966 and continued to be in use until the mid 2000s. Konkan Railway also imported Chinese and Japanese gas pressure welding machines during the construction of the Konkan railway line. Other than these, gas pressure welding is not used by IR. Metal Arc Welding is extremely rare.

Q. Who makes rails for IR?

A lot of rails come from SAIL (Steel Authority of India), a public sector company which makes rails at its Bhilai Steel Plant (now the second largest rail supplier in the world. It supplies the basic 13m, 26m, and 80m rails, and is now manufacturing 260m welded rail panels as well. The private sector company Jindal Power and Steel has recently started producing and supplying 260m rails.

In addition, rails have often been imported by IR, e.g., from British Steel, Penang (China), and Stela Group (Poland). Some additional private sector companies had plans to enter the arena as well. The CORUS group was involved as consultants for SAIL, and Via Pomini had been contracted by the Bhilai Steel Plant for equipment design and automation, etc. Status of these involvements is not known at the moment.

Q. What kinds of rail joints does IR use?

Fishplated joints are the most basic joints seen, on lines where there is no track-circuiting, and no welded rail in use. Fishplated joints are so called because of the use of a fishplate, which is a bar that is attached by means of bolts (fishbolts) to the rails on either side of the joint. Usually there are two bolts securing the fishplate on either side. There are variations in the basic fishplate design to account for different weights of rails, and joints in special situations such as on sharp curves, at points, etc. For 60kg/m track, while the rail specification is very close to Revised British Standard, the fishplates (and fishbolts) are considerably stronger than the British standard specifies.

Combination fishplates are used to secure rails of different weights or different profiles together at a joint. Expansion joints or "rail expansion joints" are provided in welded rail sections and other places where it is desirable to allow the rails to expand and contract with the varying temperature. (See below.) Special fishplates are used for expansion joints (different types for different weights of rails, and also for simple expansion joints and special expansion joints with central rail pieces.

Insulated rail joints are used in places where it is essential to keep adjacent rails electrically insulated from each other for the purposes of track circuiting or signalling. (See the section on interlocking and track circuits.) Insulated rail joints (also known as "block joints" in some cases) are of three types. Class A joints were an older type, made of wood to achieve the electrical insulation. Class B joints used Nylon 66 (and are hence known as "Nylon insulated rail joints") to achieve the insulation. Class C joints are glued insulated rail joints and are now used as the standard across the entire network. G3(L) joints are longer and use 6 fishbolts; G3(S) joints are shorter, and use 4 fishbolts.

Q. What are expansion joints?

Expansion joints (or 'switch expansion joints') are joints provided at intervals in the track to allow space for rails to expand in hot weather. Earlier expansion joints were simply gaps between the ends of adjoining rails. These gaps result in a lot of violent shocks to the vehicles riding on the rails and besides, limit the lengths of rails that can be used. Newer expansion joints have the neighbouring ends of rails mitred or tapering with diagonal cuts so that as they expand they can slide past one another to some extent. This allows for longer welded rail segments to be used and also reduces the shock to passing vehicles. In some cases, such as girder bridges with long (over 30.5m) spans, special expansion joints are provided where a short central piece of rail, not keyed to the sleepers, is provided in between the two long rails that meet at the joint; the central rail is also mitred as are the two long rails on either side, so that the effective expansion gap available is twice as long as in the standard mitred expansion joint.

Thermal expansion of rails is often arrested by the provision of heavy RCC sleepers (280kg weight) and firmly clipping the rails to the sleepers. This prevents thermal expansion from propagating to the ends of the rails, except for a section near the ends ('breathing length') that is allowed to expand. Such expansion joints are provided once every 3km to 4km on most sections today, and especially close to distant signals or advanced starters where track-circuiting begins.

Q. What are the usual neutral temperatures for continuously welded rail? What equipment does IR use for track destressing?

IR divides the country into five zones based on the normal temperature variation expected in each region. The maximum rail temperature difference is about 70C (ranging from a minimum of -5C to a maximum of 60C or so — the rail temperature can be several degrees higher than the ambient temperature. The neutral temperature or stress-free temperature for CWR is usually fairly high, 40C or even higher in some locations depending on expected summer temperatures — it is usually 5 to 10C higher than the expected mean temperature for the zone's range.

Track destressing is carried out when the ambient temperature is high, not much below the maximum that is normally attained in the area. Switch expansion joints (SEJ) are provided at the ends of long welded rails to allow for the cumulative thermal expansion movements of the ends of the rails. Most SEJs allow for a movement of the ends of the rails of about 120mm, but there are some SEJs with a maximum gap of about 190mm.

Because of the high neutral temperatures, IR does not issue speed restrictions in the summer for reasons of excessive ambient temperature as railways in some other countries do. But track patrollers continuously monitor the track in the daytime in the summer (11am - 5pm) to verify that no section of track is developing a tendency to buckle. Rail fasteners used by IR are of the type that completely resist longitudinal motion of the rails.

A lot of track destressing is still done manually on lesser and branch lines, but IR has moved to using hydraulic track tensors to destress and pretension rails on its main and trunk routes. Lateral and vertical adjustments are usually done manually using hammers or mallets and crowbars to lift and move the rails after they are unfastened from the sleepers. The unfastening and fastening of the sleepers is also usually done manually.

For some more information, see: Determining the Stress-Free Temperature in the field.

Q. What kinds of sleepers are used by IR?

IR predominantly uses prestressed (pretensioned) concrete sleepers. These are of mono-block construction. Twin-block, reinforced concrete sleepers were also used in certain sections, but these have been gradually replaced with the mono-block ones during track renewal. Concrete sleepers came into use in the 1970s. Standard prestressed concrete sleepers are available for a number of configurations for use in turnouts.

Post-tensioned concrete sleepers existed in the past; these were manufactured at the factory in Subedarganj, Allahabad (now Prayagraj).

Steel channel sleepers, consisting of two steel channels placed back to back, are used on bridges. These use special polymer or rubber pads between the bridge girders and the sleeper bottom and also below the rails for damping. Although these are now being phased out in favour of composite sleepers during renewal. Steel channel sleepers were prone to corrosion and also had issues with their large (more than 10) fitting points, as well as some problems with track-circuiting.

Cast iron sleepers ('CST-9') were also widely used. They were not very suitable for high-speed traffic and so were not usually seen on the mainline BG sections. The earlier 'pot sleepers' were especially prone to problems; newer cast iron sleepers (with ends that had two pockets) were much more laterally stable. Steel trough sleepers ('ST') were very also common, especially for many high-traffic BG routes. Steel sleepers of various designs were also been used for MG and (by reusing discarded MG sleepers) for NG too.

The most common sleepers used to be the wooden sleepers, but these are now not seen much anywhere except on some bridges (where they are being replaced, see below), and at remote locations. These may be untreated (from durable woods like teak or sal that have natural resistance to vermin and weather wear) or treated (from softer woods such as deodar, usually heat- and pressure-treated with chemicals such as creosote and furnace oil). Treatment plants for wooden sleepers were at Dhilwan (Punjab), Naharkatia (Assam), Olvakot (Kerala), and Clutterbuckganj (UP).

Wooden sleepers were used on bridges and turnouts because they were very easily cut and sized on site to fit the peculiarities of the particular stretch of track. Wooden sleepers were also preferred for bridges because they are lighter compared to the concrete sleepers, and provide additional damping for vibrations.

(04/2001) RDSO had developed some sleepers of synthetic material (fibreglass-reinforced plastic) in conjunction with the Defence Research and Development Organization, which were being used in trials on some bridges and at other places. These sleepers were developed in response to a Supreme Court verdict mandating that wood should gradually be phased out as a material for railway sleepers (environmental concerns). These trials were discontinued and the sleepers discarded as they turned out to develop dents and wear marks or grooves very quickly — within two to three years — below the rails (at the rail seats).

(06/2018) RDSO made modifications to the synthetic material to be used (addition of better glass fibres and foamed urethane) in these composite sleepers. As a result, they now have better wear and tear characteristics and are now being deployed on bridges across the network.

Another experimental version involved sleepers made of a composite material consisting of regrind resin, rubber recycled from discarded from automobile tires, and compacted HDPE film. These (named 'Tietek') were developed in conjunction with a private firm and were deployed in trials on some bridges of the NR and ER. Results of these trials are not known.

A few stretches of track have ballastless concrete beds with no sleepers (see below).


Some of the earliest tracks of the GIPR used stone sleepers. Wood quickly came into widespread use, however, and the frantic pace of railway construction in the late 19th century and early 20th century caused some serious deforestation in many areas.

Q. What rail fasteners does IR use?

IR uses various kinds of Pandrol design fasteners, ERC Mark III (850-1100kg toe load), and ERC Mark V (1200-1500kg toe load) (the latter developed by RDSO). Pandrol 'J' clips, often yellow in colour, which have a lower profile and lower toe load), are used where they need to be removed and reinserted easily and where ordinary clips might interfere with the fastening of fishplate bolts.

IR also uses Grooved Rubber Sole Plates (GSRP) underneath the fasteners to better dampen and absorb uneven vibrations. These plates are made using natural rubber (in a Ribbed Smoked Sheet, grade 1 to 4) or a blend with compounded/vulcanized Styrene Butadiene Rubber and/or Poly Butadiene Rubber.

Q. What sleeper spacings does IR use?

Broad Gauge

Most BG mainline sections now have about 1660 sleepers per km (about 60cm spacing); the earlier standard used to be 1538 sleepers per km (about 65cm spacing). BG branch lines and sidings may have 1540 sleepers per km (about 65cm spacing). 1340 sleepers per km (about 75cm spacing) were also the norm on branch lines for some time.

The older standard was 1307 sleepers per km (about 76cm spacing). Minor or lightly used BG lines used to be built with about 1154 sleepers per km (about 87cm spacing). These figures applied mainly to the traditional wooden sleepers.

Broad Gauge Routes and Sleeper Densities
Traffic Density in GMT/yr Track Classification
A B C D Spl D E
> 20 1660 1660 1660 1660 1660 1660
10-20 1660 1660 1660 1660 1660 1540
< 10 1660 1540 1540 1540 1540 1540
Loop Lines 1340 1340 1340 1340 1340 1340

Metre Gauge

MG sections with heavy traffic had about 1583 sleepers per km (63cm spacing); branch lines had about 1332 sleepers per km (75cm spacing); and minor MG lines had around 1167 sleepers per km (86cm spacing).

Narrow Gauge

NG sections varied (and continue to vary) a lot, but the commonest spacing is 11122 sleepers per km (89cm spacing).

Sleeper spacings are smaller in some cases on curves, near points, etc. The spacings are usually larger on bridges. Metal sleepers may in some cases were laid more sparsely than wooden sleepers. While the minimum sleeper density is M+4 for short welded rail (see below for explanation of notation), for up to 6 rails abutting an SWR section, the sleeper density is M+7.

Q. What does the notation 'N+4' or 'M+3', etc., mean in describing sleeper densities?

This notation is an old one. The 'N' or 'M' in this stands for the length of a rail in yards. The additional number specified represents the excess of the number of sleepers over the number of yards for a rail. E.g., 'N+3' for 11-yard (33') rails indicates 14 sleepers (11 + 3) for each rail. This was a convenient formulation, especially when rails were manufactured to sizes of 11, 12, or 14 yards. Before the days of mechanized track laying, it was common to see track laid where the sleeper density was not uniform, with some bunching up of sleepers towards the end of each rail, with adjacent sleepers at the ends of neighbouring rails being less than a foot apart in some cases.

Q. What dimensions of sleepers does IR use?

Concrete BG sleepers dimensions are usually 2.75m x 0.25m x 0.2m. BG wooden sleepers were 2.75m x 0.25m x 0.13m. MG wooden sleepers were 1.8m x 0.2m x 0.115m. NG sleepers are usually of the same thickness as MG sleepers, and are often made by cutting MG sleepers (sometimes discarded ones) to size and adding a new seat for the track.

Most sleepers on the Darjeeling Himalayan Railway are wooden, of size 5' x 7" x 4-1/2", although 'remanufactured' MG steel sleepers are also used. On 2' NG, sleepers are usually 4-1/2' x 8" x 4" or 4-1/2' x 7" x 4".

Q. What is the relationship between speed, turning radius, and track cant? What are the cant excess/deficiencies specifications for IR tracks?

Super-elevation, or cant, is provided to counteract the centrifugal tendency of trains on curves. On a canted curve (where the outer rail is higher than the inner one of the curve), the weight of the vehicle provides a component that counteracts the centrifugal tendency. Cant excess refers to the condition where the cant or superelevation is too much for the permitted speeds on the curve, while cant deficiency refers to the condition where the track is not canted enough for the speed of the trains.

On BG track, cant excess and cant deficiency tolerances are 75mm. In special cases, cant deficiency can be as high as 100mm on sections with speeds of over 100km/h on 'A' and 'B' category routes. Maximum cant is 165mm on 'A' and 'B' routes, and 140mm on 'D' and 'E' routes.

The formula relating the maximum speed on a curve with the cant and cant deficiency is:

Max. speed = 0.27 * sqrt((cant + cant deficiency) * radius)

where the cant and cant deficiency are in mm, the radius of the curve is in meters, and the speed is in km/h. Using this formula it may be seen that with a cant of 165mm and cant deficiency of 75mm, the radius for a curve allowing 100km/h traffic is 571.6m. Any curve sharper than this must have a speed restriction on a 100km/h section.

Q. What are the typical placement specifications for check rails or guard rails?

Wheel flanges on IR are typically about 28mm thick (new). The distance between the inner faces of wheels is typically 1600mm (BG). Check rails used to prevent wheels from climbing the rails at sharp curves are kept at a distance of about 44mm-48mm from the outer rail, allowing about 4mm tolerance for wear on the check rails.

Check rails at level crossings (intended to keep a gap in place for the wheels to pass through where the tracks cross the road surface) are typically placed to provide a gap of 51mm-57mm. This allows sufficient lateral movement or play for the wheels, but is small enough not to trap the feet of cattle or cause other problems for the road traffic.

Guard rails on bridges are usually placed to provide a gap of 250mm from the running rails.

Q. What kinds of ballast does IR use?

For all high-traffic lines, IR uses machine crushed hard stone ballast, usually from locally quarried granite stone, or crushed basalt. In the past, broken brick, slag from metal processing, cinders, and waste construction material were also used.

The ballast is of a 6.5cm nominal size (not more than 5% retained on a 65mm square sieve, 40%-60% retained on a 40mm square sieve, and at least 95% retained on a 20mm square sieve). In the past, ballast of 5cm nominal size was extensively used, and smaller ballast of 4cm - 2.5cm were used for iron or steel sleepered tracks and points.

The ballast layer is 0.35m in newer track or where renewals take place. 0.3m layer is also found on older tracks. In the past, the ballast layer was 0.15m - 0.25m thick on most lines.

The sides of the ballast layer generally slope at a 1.5:1 incline.

A few sections of IR have ballastless concrete bed track: much of the Calcutta Metro, a few sections of Konkan Railway, the second phase of the Chennai MRTS project (about 8km of the elevated portions of the route, with design speeds up to 100km/h). Earlier (1980s?), this had been experimented with on very limited sections of some WR and NR lines but had not been found suitable for large-scale adoption with the materials and technology of the time.

Q. What sort of sub-ballast, blanket, and sub-grade layers are provided in the track formation?

IR generally does not use a separate sub-ballast layer below the ballast layer. A blanket layer of coarse, granular material is usually provided directly below the ballast layer. Blanket layers are not provided for tracks on rocky beds, or on well-graded gravelly or sandy beds.

Blankets of at least 45cm thickness are provided for tracks laid on poorly graded gravel or sand beds, or on silty gravel or silty / clayey gravel beds. Blanket layers of 60cm are required for clayey gravel, clayey sand, silty sand, or clayey / silty sand beds. A 1m-thick blanket is provided for silt, silty clay, or clay of low plasticity or in conditions where the underlying rocks are of a type known to be excessively susceptible to weathering. The blanket layer is generally composed of well-graded sandy gravel or crushed rock with specified distributions of size and curvature. Mixtures of fines (metal, plastic, etc.) from industrial applications are used in specific proportions in some cases, as are certain other waste materials that conform to specified mechanical, chemical, and geometric requirements.

The subgrade is generally built up from a mixture of soil and stone fragments, cobbles, and waste materials, crushed brick, etc. The blanket and subgrade are built up at a slope of about 2:1. The entire embankment may rise to 6m with most ordinary kinds of materials used for the blanket and subgrade. In case the subgrade is thicker than 1m or so, usually a 30cm layer of compacted soil is provided for every 1m-3m of the subgrade thickness.

Q. What are ‘GeoJute’ and ‘GeoGrids’? How does IR prevent soil erosion in the areas where track is laid?

Erosion of the soil around a track formation can be quite dangerous as the track may subside or warp and move. In many cases IR simply encourages the local shrubby vegetation to grow in the areas near the track to stem the erosion. Where severe erosion is a problem, ‘GeoJute’ has been used. This is an ecologically safe material made of jute yarn with a coarse open mesh structure. This is placed on the affected portions of the embankment or cutting after removing clods, large stones, etc., and appropriate scrubby vegetation is seeded in the area. The jute yarn is biodegradable and disappears after a while, but by that time the vegetation has had a chance to take root and grow firmly in the protected soil.

In rare cases where vegetative root growth is thought to be insufficient to stem the erosion of the soil, a synthetic root matrix reinforcement system may be used. Known as ‘GeoGrids’, these flexible, synthetic meshes of simply extruded, unoriented and unstretched polymer materials are placed in the top layer of the soil to provide erosion resistance both by its own presence and by strengthening the root matrix of the local vegetation.

These GeoGrid polymers are non-biodegradable, and quite stable, resisting ultraviolet exposure and tolerant of very high and low temperatures. Boulder retention in some places is augmented by the deployment of bi-axially oriented GeoGrid meshes to anchor medium to large boulders. In a few cases, IR has also resorted to ‘hydroseeding’, involving the sprinkling of seeds of fast-growing grasses and scrub vegetation with specially formulated mulch and fertilizer mixtures.

Self-stabilizing Track

Konkan Railway has developed something they call self-stabilising track, which aims to reduce or even eliminate the problem of ballast being de-compacted and dispersing under the action of vibrations set up by moving trains.

The ballast in this system is laid on the track bed pre-compacted with constraining 'cages' that hold large amounts of ballast together. These cages or ballast elements are of several modular shapes, 'L' or 'T', etc., and are placed in interlocking ways on the track bed. The effect is not only to prevent the ballast from spreading under the action of vibrations, but to improve ride quality by changing the vibration characteristics since the inertial mass responding to the impact from the train is larger. A thin sheet of rubber or polyethylene between the sleepers and the top of the track bed further modifies the vibration characteristics. The ballast elements are constructed of such a shape that the vibrations tend to wedge them more firmly together. The expectation is that ballast maintenance will be much reduced for such tracks.

Q. What tolerances of gauge does IR permit?

Broad Gauge: Deviations allowed from nominal gauge: -5mm to +3mm on straights and curves over 350m radius, and up to +10mm on curves sharper than 350m radius. (The older specifications were: On straight sections, a deviation of +/- 6mm; and on curves a deviation of up to +20mm/-6mm.) High-speed sections (130+ km/h) have tighter tolerances of +/- 2mm.

Meter Gauge: Deviations allowed from nominal gauge: -2mm to +3mm on straights and curves over 290m radius; and up to +10mm on curves sharper than 290mm radius. (The older specifications were: On straight sections, a deviation of +/- 3mm, and on curves a deviation of up to +15mm / -3mm; on particulary sharp curves the deviation could be up to +20 mm.)

Narrow Gauge: Deviations allowed from nominal gauge: -3mm to +3mm on straights and curves over 400m radius; up to +10mm on curves between 100m and 400m radius, and up to +15mm on curves sharper than 100m radius. (The older specifications were: On straight sections, a deviation of +6mm / -3mm; on curves +15mm / -3mm; especially sharp curves could have a deviation of +20mm.)

Q. What are the nets one sees on rock faces or hillsides abutting railway lines in some areas?

In areas where rock falls or landslides are common (particularly on the Konkan Railways), IR uses meshes or nets fixed to the rock faces or the hillsides -- these are ‘stitched’ to the hillside at frequent intervals. They act to trap and stop, or slow down falling or sliding rocks and boulders so that they either do not fall all the way down, or lose their kinetic energy and fall without infringing the tracks.

Generally the nets are made of polypropylene ropes of 10mm-16mm diameter with high thermal, abrasion, and ultraviolet resistance. The mesh size is from 100mm to 300mm depending on the area, and the typical size of the fractured or falling rocks. These are appropriate for retaining and slowing small to medium sized boulders and the mesh strength is about 6-8 tons/m2. In some areas steel nets made of high-strength galvanized steel wire ropes are used. These ropes have a breaking strength of 4 tons and provide a mesh strength of 13-14 tons/m2 to retain large boulders. These have a design life of over 20 years.

Q. What is the ‘Raksha Dhaga’? What other methods does IR use to warn of landslides and rockfalls?

‘Raksha Dhaga’ or literally, ‘Safety Thread’, is a device pioneered by the Konkan Railways in landslide-prone areas. It consists of a wire attached to sensors which can be tripped when the wire is moved excessively or snapped by a falling rock. The sensors when tripped activate lights and hooters 0.5km away so that approaching trains can safely stop before the location of the landslide. These are used in several stretches on the KR route in cuttings and in unlined tunnels.

In addition, KR has pioneered the use of electronic inclinometers to detect earth slippages in areas prone to landslides, connected to a similar warning system as in the Raksha Dhaga.


Q. How is track maintained?

Permanent way maintenance is largely done by gangs consisting of gangmen under the supervision of a gangmate. The gang goes down its assigned section of track (the gang beat or beat section), inspecting track and performing normal routine maintenance. A patrolman may be separately deputed to perform visual inspections along the length of a section of track by walking alongside it (two patrolmen in ghat or jungle areas). Typically the patrol may cover 6km - 10km of track.

The schedule and track sections to be monitored by gangmen and patrolmen is specified in a Patrol Chart prepared by the Divisional Engineer. This chart also indicates when and where the drivers of trains running to schedule may expect to meet gangmen. Patrolmen and gangs carry Patrol Books in which they record the status of the track and any maintenance they perform on it.

The gang is equipped to deal with minor problems such as fixing small deviations in gauge or elevation of the rails, rearranging ballast, etc. If problems are discovered with the permanent way that cannot readily be fixed by the gang, the details are reported to the station master of one of the adjacent block stations, and temporary engineering speed restrictions are put in place for the track. Trains going through that section are then subject to caution orders issued by the stations at either end.

A bigger maintenance of way crew with appropriate tools and machinery then works on repairing the track while it is protected by being restricted. In some cases traffic on the line may have to be completely stopped. Replacing ballast or sleepers, adjusting the rail profile by grinding, joint lubrication, rail creep adjustment, replacing short sections of damaged rail, welding rails, etc., are some of the other maintenance tasks that come up.

The regular patrolling of track is very important in order to maintain safe conditions for trains. If a patrolman or gang is unaccountedly late or if a patrolman misses his beat for some reason, caution orders are usually issued advising drivers to be alert for track defects and restricting trains on the affected sections of track to 40km/h (daytime, clear visibility) or 15km/h (night, bad visibility).

The permanent way inspector (PWI) for a division has ultimate responsibility for the condition of the permanent way under his jurisdiction. The PWI and his staff undertake separate regular inspection tours of the various lines, often in a motor trolley or inspection car. (In the past manually pushed trolleys were used quite often, but their use is declining now.)

Track maintenance machines, for instance tie tamping machines, ballast cleaning machines etc. are also used. (See below)

Q. What is ‘beater packing’? What is included in the maintenance carried out by gangs commonly seen on the tracks?

The most common system of routine manual (non-mechanized) track maintenance is known as through packing or beater packing (from the name of the tool used for packing ballast, a ‘beater’). This includes the following steps:

  1. Opening of the road: ballast is unpacked, fittings and fastenings of the rails loosened.
  2. Examination of track: Rails, sleepers, fastenings are carefully examined for signs of wear, corrosion, rust, dust and dirt, etc. Wire brushes are used for cleaning; jimcrows and other tools to rectify minor kinks or other defects. Sleepers are examined for signs of splitting or decay. Minor repairs such as replacement of fastenings, rail lubrication, etc., are performed.
  3. Squaring of sleepers: Sleeper hammers are used to adjust sleepers to the proper position.
  4. Slewing of track to fix the alignment of the rails.
  5. Gauging: the gauge between the rails is carefully measured and adjusted as necessary.
  6. Sleeper packing: Each sleeper is uniformly and firmly packed so the rails are the correct relative levels and to ensure the sleepers have no voids between themselves and the trackbed. This is where ‘beaters’ are used. These are long rod-like tools with an end used to pack the ballast. The beater is held by the hands and raised to about chest level and then plunged downwards to pack the ballast.
  7. Re-packing of joint sleepers.
  8. Boxing the ballast section and cleanup.

Another system of manual ballast packing called ‘measured shovel packing’ used to be common but is now not in use.

In addition to ballast packing, gangs perform a variety of other cleaning and maintenance jobs, such as maintaining drainage, adjusting cess level (too high affects drainage, too low results in ballast spread and wastage), removing weeds and stones, etc.

Crews also pick up slack in the track. Slack refers to the condition where there is insufficient ballast or a gap developing between the track and the trackbed, or subsidence of the track, because of a yield formation in high banks and cuttings, at approaches to bridges, on badly aligned curves, where ballast is poorly laid or insufficient, or where there are drainage defects causing subsidence problems. Slack is picked up by opening the track and repacking the ballast.

Track Defects

An explanation of track defects in general is beyond the scope of these pages. Please consult any current reference book on permanent way technology. A list of track defect indications is provided at the signs and symbols page.

Q. What is ‘through’ or ‘scattered’ renewal?

Complete Track Renewal (CTR) refers to the most thorough track replacement regime where rails, sleepers, etc., are fully replaced. Through Rail Renewal (TRR) refers to the replacement of rails in a given section of track, while Through Sleeper Renewal (TSR) refers to the replacement of sleepers. Similarly, there are Through Turnout renewal (TTR), Through Fitting Renewal (TFR), Through Weld Renewal (TWR), and Through Bridge Timber Renewal (TBTR). Each of these has a more thorough (‘primary’) and less thorough (‘secondary’) versions, hence you see the acronyms like ‘CTR(P)’ for ‘Complete Track Renewal - Primary’, or ‘TSR(S)’ for ‘Through Sleeper Renewal - Secondary’.

Additionally there are ‘Casual’ renewals, which refers to renewals of any kind that happen not on a predetermined schedule but as determined based on patrolling and inspection of tracks, in small continuous stretches. Finally, ‘Scattered’ renewal (SR) refers to ad hoc replacements that happen at isolated points.

Q. What are Rational Formulae? What is Maflin’s Formula? What is the Special Committee Formula?

These are various formulae for calculating the gang strength required to perform maintenance of different kinds on a section of track.

Maflin's Formula, adopted in 1931, is a very simple one (number of gangmen = 2.5 x ‘unit per mile’ x length of track, where the ‘unit per mile’ factor depends on the kind of traffic carried on the track). It assumes a standard requirement of manpower regardless of the track gauge.

The Revised Maflin's Formula was adopted in 1962 following the recommendations of the Lobo Committee in 1959. In this, rather than using the length of track directly, the length is specified in Equated Track Miles (ETM), which depends on traffic density, type of track formation and gauge, special considerations such as curved alignment, and factors such as the annual rainfall in the region.

The Special Committee Formula was adopted in 1979 (as the name suggests, on the recommendation of a special governmental committee). It specifies the gang strength as 0.95 x M x K x E, where M is the Manpower Factor (1 for NG, 1.21 for MG, 1.47 for BG), K is the Correction Factor accounting for modernization of track and methods of maintenance (for instance, different factors are used for SWR/LWR track, types of fishplates and sleepers, whether ballast is packed manually or mechanically, etc.), and E is the Equated Track Kilometers (ETKM) which includes factors for the traffic density and type of track formation, etc., over the basic track length.

The newer Rational Formulae were developed because the Special Committee Formula above was felt inadequate to account for differing manpower availability (skill sets, age distribution) in different regions or zones, increasing use of casual labour and private contractors for certain track maintenance activities, etc. In 1996, another committee was constituted by the Railway Board to look into this matter and to recommend changes to the Special Committee Formula.

These new Rational Formulae are much more involved, and account for a wide variety of factors in terms of the nature of the maintenance work, the type of track and traffic carried on it, the distribution of casual and contracted labour for permanent way operations, etc. The Rational Formulae are actually many different formulae, for each kind of maintenance operation, and they also specify the equivalence of different kinds of work for the purposes of computing wages and so on. The latest set of Rational Formulae were adopted in 2006.

Q. Does IR use mechanized means for track laying and maintenance?

IR uses a wide variety of machines for track laying and maintenance, though lots of track laying and renewal is still done manually.

Tie tamping machines are common: Unimat models (by Plasser) tamp one sleeper at a time and can pack sleepers on normal track and turnout; Duomat models tamp two sleepers at a time on normal track. CSM is another tie tamper used by IR; it has a cab that moves continuously while the tamping machine itself starts and stops over alteranate sleepers to tamp them two at a time — this reduces driver discomfort. CSM tampers are the most common ones used by IR today.

(04/2018) Newer machines called 09-3X Dynamic Tamping ‘Express’ made by Plasser have been inducted and are expected to take over the bulk of the work on trunk lines. These can tamp three sleepers at a time, measure pre & post track geometry, correct the track to required geometry, stabilize and measure post tamping track parameters. IR has ordered a total of 42 such machines for deliveries into 2022.

Ballast cleaning and regulating machines are also used these days. The most common cleaning ones are RM-76 and RM-80 by Plasser. The ballast regulating machines, which help transfer ballast and keep an even profile across the entire trackbed, are made by Kershaw.

Dynamic Track Stabilizer (DTS) machines are also used to measure and correct track geometry and ‘settle’ tracks faster. These feature KTA-1150L, 473 bhp prime movers from Kirloskar-Cummins.

Plasser brand machines form the bulk of the track-laying fleet. These include the ‘PQRS’ or Plasser Quick Relaying System which consists of self-propelled portal cranes, which travel on a wider gauge, called auxiliary track, laid temporarily, outside the track to be renewed. Their capacity for track renewal is about 400m per effective traffic block hour. The manufacturers are Plasser and Theurer, BEML, and Simplex.

‘TRT’ or Track Relaying Train machines (also sometimes Track Renewal Train), capable of continuously relaying track at a few hundred meters an hour are also used. These are made by 'M/S Harsco Track Tech' (earlier 'Fairmont Tamper' and still earlier, called 'Tamper Corporation') of USA. (One machine of this type was purchased initially from Russia, but that was a one-off purchase. In 2004, there were four of these, with more inducted over the years.)

The ’T-28’ is a point and crossing renewing machine made by Ameca, Italy, used for re-laying track at turnouts and points.

BEML has recently been supplying IR with BG track-laying machines. These machines can remove old rails, and lay new BG track (including concrete sleepers), assembling the rails and sleepers into panels before laying the track.

A machine consists of two large vertical frames which are connected by a bridge. The bridge can be moved up and down between the side frames. A diesel engine and hydraulic pumps are installed on the bridge. The vertical frames rest and move on rails of an auxiliary track of 3.4m gauge. The wheel base is about 2.4m. It weighs about 12t, and can move at about 14km/h.

The machine can lift sleepers and track up to 9t. Panel lifting is accomplished by the use of four independently controlled hydraulic scissors mechanisms. Rails and sleepers can also be moved laterally through hydraulic positioners. The equipment attached to the bottom of the bridge is connected via a turntable, allowing for rotational movement of the loads being lifted. Sleepers are gripped by hydraulically operated angle grippers.

The machine uses a 6-cylinder vertical inline KOEL diesel engine (HA694) for its motive power. In addition to laying track, the machine can load and unload itself from BFR flat wagons.

For track inspection and monitoring by mechanical means, IR also now uses laser-based contactless track-recording cars for measuring rail corrugation. Portable accelerometers and optical rail profile measurement systems are also used.

Q. What is included in the 3-tier maintenance regime?

The three-tier system divides responsibilities for track maintenance as follows:

  1. On-Track Machines (OMU): Mechanized maintenance (see above) including systematic tamping, intermediate tamping, shoulder ballast cleaning, ballast profiling and redistribution, track stabilization, and periodic deep screening of ballast.
  2. Mobile Maintenance Units (MMU): These are of two types. MMU-I refer to the permanent way units that are assigned to deal with spot tamping, in-situ rail welding, casual renewal and repairs, overhaul of Level Crossings, glued joint replacement, and machining of rails including cutting, drilling, grinding and chamfering. Normally there is one MMU-I unit for each Permanent Way Inspector's office. MMU-II refers to the units specially assigned for reconditioning turnouts, switches, joints and other such intricate trackwork.
  3. Sectional Gangs: These are permanent way gangs that handle patrolling (including keyman's daily patrols, hot and cold weather patrols, and monsoon patrols), and watching vulnerable locations, bridges, turnouts, switch expansion joints, level crossing approaches, etc. In addition these teams handle minor maintenance including temporary repairs, lubrication of elastic rail clips (ERC) and joints, changing rubber pads, liners, and clips, minor cess repairs, cleaning drains, boxing ballast, manual adjustments of loops and creep / gap adjustments, cleaning crib ballast and handling other drainage issues, de-weeding, removing boulders and other debris, and pre- and post-tamping attention. Periodically, the sectional gangs also carry out maintenance such as picking up slack in the permanent way.

Q. What are the small vertical sections of rail that can be seen embedded in the track works or a little distance away from the tracks every so often?

These small vertical pieces of rail (or other structures such as a small cement post), usually painted yellow or white, are monuments or vertical datum indicators. They have marks on them that indicate the correct intended height of the rail head at that location on the track. When track maintenance crews adjust track for its level, they use these indicators as the reference to which to adjust the rails. (Of course, other considerations apply in special cases such as at curves, where the track's cant has to be taken into consideration.)

These indicators are also used to measure the longitudinal movement of long welded rails. The indicators are usually buried quite deep into the earth so that they do not shift around easily. Sometimes the track level is indicated painted on a nearby permanent structure instead.

There are also water level indicators in some areas, which are upright pieces of rail with graduated markings on them in red, yellow or light green, and dark green. These serve as indications to locomotive and EMU drivers during flooding. Generally speaking normal speeds are permitted if the (dark) green section of the rail is visible. Reduced speeds and cautious operating are indicated when the water level rises to the yellow or light green mark, and trains are not permitted to proceed into sections that are so deeply flooded that the water level reaches the red mark, or covers the water level indicator entirely. (EMU drivers especially tend to be very familiar with the location of each of these indicators and will know when they are submerged and not visible.)

Q. What are the indications sometimes seen written or painted on rails, e.g., O+, C-2, etc?

These are defect indications marked by the permanent way gang. Please see the page on miscellaneous signs and indications for these.

Q. What are the boards seen by the side of the tracks marked ‘AEN/TNA - AEN/KYN’ or some such?

These are jurisdictional boundaries for sections, subdivisions, or divisions in charge of maintaining the permanent way. Please see the page on miscellaneous signs and indications for these.

Q. What are the signs seen by the side of the tracks marked 'G-2 / 1+1+12' or some such?

These are gang beat boundaries for the gangs maintaining the permanent way. Please see the page on miscellaneous signs and indications for these.

Q. Sometimes the sides of rails appear to be painted. Why is this done?

Normally, rails do not need to be painted as the expected life span resulting from the effects of wheel wear and fatigue is such that corrosion is not a significant problem. In some areas, however, corrosion of rails, especially on the inside of the rail foot below the liners, or on the sides, can be quite severe, and may result in the need for premature renewal of the tracks even if the rails are otherwise not worn or fatigued by the traffic conditions. The problem is worse when the spots where the corrosion makes the rails weak move out of the sleeper seats during activities like track de-stressing.

Corrosion happens in coastal areas and regions such as the Sambhar Lake area where there is high salinity. Damp tunnels are also places where corrosion can be higher than normal.

To prevent such corrosion and to increase the life of the rails, IR practice is to paint the rails on the sides and on the foot in affected areas.

In the past, since IR used direct discharge toilets for passenger trains, corrosion resulting from toilet waste was a significant problem on some lines, and especially at approaches to major stations where many busy lines converged. This problem is less common in recent times as passenger coaches now come fitted with a ‘bio-toilet’ that treats waste before discharge.

Q. Where are the oldest rails to be found on IR?

Most of the very old tracks have by now been relaid and renovated, so that it is very hard to find very old rails. Abandoned lines (especially metre-gauge and narrow-gauge sections) also have old rails left intact. The Bombay Port Trust railway tracks between Dockyard Road and Wadala/Raoli might be among the oldest. Bullhead rails from the late 19th century or early 20th century were still to be found in some areas (e.g. peripheral sidings at Dadar, near Thane, etc.) but many have by now been replaced.