Arailroad tie,crosstie (American English),railway tie (Canadian English) orrailway sleeper (Australian andBritish English) is a rectangular support for therails inrailroad tracks. Generally laid perpendicular to the rails, ties transfer loads to thetrack ballast andsubgrade, hold the rails upright and keep them spaced to the correctgauge.
Railroad ties are traditionally made ofwood, butprestressed concrete is now also widely used, especially in Europe and Asia.Steel ties are common on secondary lines in the UK;[1]plastic composite ties are also employed, although far less than wood or concrete. As of January 2008, the approximate market share in North America for traditional and wood ties was 91.5%, the remainder being concrete, steel,azobé (red ironwood) and plastic composite.[2]
Tie spacing may depend on the type of tie, traffic loads and other requirements, for example 2,640 concrete ties per mile (1,640/km) on North American mainline railroads[3] to 2,112 timber ties per mile (1,312/km) onLondon, Midland and Scottish Railway jointed track.[4]
Rails in North America may be fastened to the tie by arailroad spike. Iron/steelbaseplates screwed to the tie and secured to the rail by a proprietary fastening system such as aVossloh orPandrol are commonly used in Europe.
The type of railroad tie used on the predecessors of the first true railway (Liverpool and Manchester Railway) consisted of a pair of stone blocks laid into the ground, with thechairs holding the rails fixed to those blocks. One advantage of this method of construction was that it allowed horses to tread the middle path without the risk of tripping. In railway use with ever heavier locomotives, it was found that it was hard to maintain the correctgauge. The stone blocks were in any case unsuitable on soft ground, such as atChat Moss, where timber ties had to be used.Bi-block ties with a tie rod are somewhat similar.
Historically wooden rail ties were made by hewing with an axe, calledaxe ties, or sawn to achieve at least two flat sides.A variety ofsoftwood andhardwood timbers are used as ties,oak,jarrah andkarri being popular hardwoods, although increasingly difficult to obtain, especially from sustainable sources.[5] Some lines usesoftwoods, includingDouglas fir; while they have the advantage of acceptingtreatment more readily, they are more susceptible to wear but are cheaper, lighter (and therefore easier to handle) and more readily available.[5]
Softwood is treated, withcreosote being the most common preservative for railway ties. Other preservatives used includepentachlorophenol andchromated copper arsenate. Sometimes non-toxic preservatives are used, such ascopperazole or micronizedcopper. Newboron-based wood preserving technology is being employed by major US railroads in a dual treatment process in order to extend the life of wood ties in wet areas.[6] Some timbers (such assal,mora,jarrah orazobé) are durable enough that they can be used untreated.[7]
Problems with wooden ties include rot, splitting, insect infestation, plate-cutting, also known as chair shuffle in the UK (abrasive damage to the tie caused by lateral motion of the tie plate) and spike-pull (where thespike is gradually loosened from the tie). Wooden ties can catch fire; as they age they develop cracks that allow sparks to lodge and more easily start fires.
Concrete ties are cheaper and easier to obtain than timber[dubious –discuss] and better able to carry higher axle-weights and sustain higher speeds. Their greater weight ensures improved retention oftrack geometry, especially when installed with continuous-welded rail. Concrete ties have a longer service life and require less maintenance than timber due to their greater weight, which helps them remain in the correct position longer. Concrete ties need to be installed on a well-prepared subgrade with an adequate depth on free-draining ballast to perform well. It is a common misconception that concrete ties amplify wheel noise. A study done as part of Euronoise 2018 proved this false, showing concrete sleepers to be an average of 2dB(A) quieter than wooden ones, however with a greater acoustic sharpness on straight stretches of track. Concrete ties were however shown to be quieter than wooden ties almost universal across the audible frequency band on curves.[8] This causes train noise when over concrete ties to potentially be subjectively perceived as louder than train noise over wooden ties.
On the highest categories of line in the UK (those with the highest speeds and tonnages), pre-stressed concrete ties are the only ones permitted byNetwork Rail standards.
Most European railways also now use concrete bearers in switches and crossing layouts due to the longer life and lower cost of concrete bearers compared to timber, which is increasingly difficult and expensive to source in sufficient quantities and quality.
Steel ties are formed from pressed steel and are trough-shaped in section. The ends of the tie are shaped to form a "spade" which increases the lateral resistance of the tie. Housings to accommodate the fastening system are welded to the upper surface of the tie. Steel ties are now in widespread use on secondary or lower-speed lines in the UK where they have been found to be economical to install due their ability to be installed on the existing ballast bed. Steel ties are lighter in weight than concrete and able to stack in compact bundles unlike timber. Steel ties can be installed onto the existing ballast, unlike concrete ties which require a full depth of new ballast. Steel ties are 100% recyclable and require up to 60% less ballast than concrete ties and up to 45% less than wood ties.
Historically, steel ties have suffered from poor design and increased traffic loads over their normally long service life. These aged and often obsolete designs limited load and speed capacity but can still be found in many locations globally and performing adequately despite decades of service. There are great numbers of steel ties with over 50 years of service and in some cases they can and have been rehabilitated and continue to perform well. Steel ties were also used in specialty situations, such as theHejaz railway in theArabian Peninsula where the dry, hot climate made wood ties unsatisfactory.[9]
Modern steel ties handle heavy loads, have a proven record of performance in signalized track, and handle adverse track conditions. Of high importance to railroad companies is the fact that steel ties are more economical to install in new construction than creosote-treated wood ties and concrete ties. Steel ties are utilized in nearly all sectors of the worldwide railroad systems including heavy-haul, class 1s, regional, shortlines, mining, electrified passenger lines (OHLE) and all manner of industries. Notably, steel ties (bearers) have proven themselves over the last few decades to be advantageous in turnouts (switches/points) and provide the solution to the ever-growing problem of long timber ties for such use.
When insulated to prevent conduction through the ties, steel ties may be used withtrack circuit based train detection and track integrity systems. Without insulation, steel ties may only be used on lines without block signaling andlevel crossings or on lines that use other forms of train detection such asaxle counters.
In more recent times, a number of companies are selling composite railroad ties manufactured fromrecycled plastic resins[10] andrecycled rubber. Manufacturers claim a service life longer than wooden ties with an expected lifetime in the range of 30–80 years, that the ties are impervious to rot andinsect attack,[11][12][13] and that they can be modified with a special relief on the bottom to provide additional lateral stability.[11] In some main track applications the hybrid plastic tie has a recessed design to be completely surrounded by ballast.
Aside from the environmental benefits of using recycled material, plastic ties usually replace timber ties soaked in creosote, the latter being a toxic chemical,[14] and are theoretically recyclable.[11] However, plastics may shedmicroplastics and leach other possibly toxic chemicals such as ultraviolet inhibitors.
Hybrid plastic railroad ties and composite ties are used in other rail applications such as underground mining operations,[15] industrial zones, humid environments and densely populated areas. Hybrid railroad ties are also used to replace individual rotted wood ties, which will result in intermingled hybrid and wood ties and continuous track stiffness. Hybrid plastic ties and composite ties also offer benefits on bridges and viaducts, because they lead to better distribution of forces and reduction of vibrations into respectively bridge girders or the ballast. This is due to better damping properties of hybrid plastic ties and composite ties, which will decrease the intensity of vibrations as well as the sound production.[16] In 2009, Network Rail announced that it would begin replacing wooden ties with recycled plastic.[17] but I-Plas became insolvent in October 2012.[18]
In 2012,New Zealand ordered a trial batch of "EcoTrax" brand recycled composite ties from Axion for use on turnouts and bridges,[19][20] and a further three-year order in 2015,[21] but then Axion filed for bankruptcy in December 2015,[22] though it continues to trade.[23] These ties are developed by Dr. Nosker at Rutgers University.[24]
Composite sleepers, manufactured from various recycled plastics, were introduced inWiltshire, United Kingdom, in 2021. They were installed as an alternative to wooden sleepers, on a bridge where concrete sleepers would have been too heavy. Although it was the first instance of plastic sleepers being installed on mainline track in the country, they have previously been used onnarrow-gauge railways.[25]
Ties may also be made fromfiberglass.[26]
An unusual form of tie is the Y-shaped tie, first developed in 1983. Compared to conventional ties, the volume of ballast required is reduced due to the load-spreading characteristics of the Y-tie.[27] Noise levels are high but the resistance to track movement is very good.[28] For curves the three-point contact of a Y steel tie means that an exact geometric fit cannot be observed with a fixed attachment point.
The cross section of the ties is anI-beam.[29]
As of 2006, less than 1,000 km (621 mi) of Y-tie track had been built, of which approximately 90 percent is inGermany.[27]
The ZSX Twin tie is manufactured by Leonhard Moll Betonwerke GmbH & Co KG and is a pair of two pre-stressed concrete ties longitudinally connected by four steel rods.[30] The design is said to be suitable for track with sharp curves, track subject to temperature stress such as that operated by trains witheddy brakes, and bridges, and as transition track between traditional track and slab track or bridges.[31]
Concrete monoblock ties have also been produced in a wider form (e.g. 57 cm or22+1⁄2 in) such that there is no ballast between the ties; this wide tie increases lateral resistance and reduces ballast pressure.[32][33][34] The system has been used in Germany[35] where wide ties have also been used in conjunction with the GETRAC A3 ballastless track systems.[36][37]
Bi-block (or twinblock) ties consist of two concrete rail supports joined by a steel bar. Advantages include increased lateral resistance and lower weight than monobloc concrete ties, as well as elimination of damage from torsional forces on the ties center due to the more flexible steel connections.[38] This tie type is in common use in France,[39] and are used on the high-speedTGV lines.[40] Bi-block ties are also used in ballastless track systems.[39]They are gauge-convertible by cutting and welding the steel bar to the dimension that suits the new gauge.
Frame ties (German:Rahmenschwelle) comprise both lateral and longitudinal members in a single monolithic concrete casting.[29] This system is in use inAustria;[29] in the Austrian system the track is fastened at the four corners of the frame, and is also supported midway along the frame. Adjacent frame ties are butted close to each other. Advantages of this system over conventional cross increased support of track. In addition, construction methods used for this type of track are similar to those used for conventional track.[41]
In ladder track, the ties are laid parallel to the rails and are severalmeters long. The structure is similar toBrunel's baulk track; these longitudinal ties can be used with ballast, or withelastomer supports on a solid non-ballasted support.
The crosstie spacing of mainline railroad is approximately 19 to 19.5 inches (48 to 50 cm) for wood ties or 24 inches (61 cm) for concrete ties. The number of ties is 3,250 wooden crossties per mile (2,019 ties/km, or 40 ties per 65 feet) for wood ties or 2,640 ties per mile for concrete ties.[3][42][43]
TheLondon, Midland and Scottish Railway specified 18 sleepers per 45-foot (13.72 m) rail and 24 sleepers per 60-foot (18.29 m) rail,[4] both of which correspond to 2,112 sleepers per mile.
Sleepers are 8 ft 6 in (2.59 m) long, 10 inches (254 mm) wide and 5 inches (127 mm) deep. The two sleepers adjacent to a joint may be 12 inches (305 mm) wide where the formation is soft or the traffic is heavy and fast. Sleepers are mostly spaced 2 ft 7 in (0.79 m) apart (centre-to-centre) but are closer adjacent tofishplated rail joints where the spacing sequences are as follows with the spacing atthefishplate highlighted.
| 45-foot (13.72 m) rails | 60-foot (18.29 m) rails |
|---|---|
| 2 ft 7 in (0.79 m) | 2 ft 7 in (0.79 m) |
| 2 ft 7 in (0.79 m) | 2 ft 5 in (0.74 m) |
| 2 ft 5 in (0.74 m) | 2 ft 4 in (0.71 m) |
| 2 ft3+1⁄2 in (0.699 m) | 2 ft3+1⁄2 in (0.699 m) |
| 2 ft0+1⁄4 in (0.616 m) | 2 ft0+5⁄16 in (0.618 m) |
| 2 ft3+1⁄2 in (0.699 m) | 2 ft3+1⁄2 in (0.699 m) |
| 2 ft 5 in (0.74 m) | 2 ft 4 in (0.71 m) |
| 2 ft 7 in (0.79 m) | 2 ft 5 in (0.74 m) |
| 2 ft 7 in (0.79 m) | 2 ft 7 in (0.79 m) |
The fractional inch spacing at the fishplate corresponds to the thermal expansion gap allowed between the rail ends.
Interurban railways of the late 1800s and early 1900s generally ran lighter rolling stock than mainline steam railways, but roadbeds were built to similar standards. Wooden ties were placed at approximately 2-foot (0.61 m) intervals.[44]
Various methods exist for fixing the rail to the railroad ties. Historicallyspikes gave way to cast ironchairs fixed to the tie, more recently springs (such asPandrol clips) are used to fix the rail to the tie chair.
In recent years, wooden railroad ties have also become popular forgardening andlandscaping, both in creatingretaining walls and raised-bed gardens, and sometimes for building steps as well. Traditionally, the ties sold for this purpose are decommissioned ties taken from rail lines when replaced with new ties, and their lifespan is often limited due to rot. Some entrepreneurs sell new ties. Due to the presence of woodpreservatives such ascoal tar,creosote orsalts ofheavy metals, railroad ties introduce an extra element ofsoilpollution into gardens and are avoided by many property owners. In the UK, newoak or pine beams of the same length (2.4m) as standard railway sleepers, but not treated with dangerous chemicals, are available specifically for garden construction. In some places, railroad ties have been used in the construction of homes, particularly among those with lower incomes, especially near railroad tracks, including railroad employees. They are also used ascribbing fordocks andboathouses.
The Spanish artistAgustín Ibarrola has used recycled ties fromRenfe in several projects.
In Germany, use of wooden railroad ties as building material (namely in gardens, houses and in all places where regular contact to human skin would be likely, in all areas frequented by children and in all areas associated with the production or handling of food in any way) has been prohibited by law since 1991 because they pose a significant risk to health and environment. From 1991 to 2002, this was regulated by theTeerölverordnung (Carbolineum By-law), and since 2002 has been regulated by theChemikalien-Verbotsverordnung (Chemicals Prohibition By-law), §1 and Annex, Parts 10 and 17.[45]
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Media related toRailroad ties at Wikimedia Commons
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