A railroad tie/railway tie/crosstie, or railway
sleeper is a rectangular support for the rails in railroad tracks. Generally laid perpendicular
to the rails, ties transfer loads to the track ballast and subgrade, hold the rails upright,
and keep them spaced to the correct gauge. Railroad ties were traditionally made of wood,
but pre-stressed concrete is now widely used, especially in Europe and Asia. Steel ties
are common on secondary lines in the UK; 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 and plastic composite. Coarse aggregate is the standard material
for track ballast, which provides drainage and resilience. On lines with lower speeds
and axle-weights, sand, gravel, and even coal ash from the fires of steam locomotives have
been used. Up to 3000 ties are used per mile of railroad
track in the US, 2640 per mile on main lines in the UK. Rails in the US may be fastened
to the tie by a railroad spike; iron/steel baseplates screwed to the tie and secured
to the rail by a proprietary fastening system such as a Vossloh or Pandrol are commonly
used in Europe. Types
Stone block The type of tie used on the predecessors of
the first true railway consisted of a pair of stone blocks laid into the ground, with
the chairs 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 correct
gauge. The stone blocks were in any case unsuitable on soft ground, such as at Chat Moss, where
timber ties had to be used. Bi-block ties with a tie rod, are somewhat similar.
Wooden Historically wooden rail ties were made by
hewing with an axe, called axe ties or sawn to achieve at least two flat sides. A variety
of softwood and hardwoods timbers are used as ties, oak, jarrah and karri being popular
hardwoods, although increasingly difficult to obtain, especially from sustainable sources.
Some lines use softwoods, including Douglas fir; while they have the advantage of accepting
treatment more readily, they are more susceptible to wear but are cheaper, lighter and more
readily available. Softwood is treated, historically using creosote, but nowadays with other less-toxic
preservatives to improve resistance to insect infestation and rot. New boron-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. Some timbers are durable enough
that they can be used untreated. Problems with wood ties include rot, splitting,
insect infestation, plate-cutting, also known as chair shuffle in the UK and spike-pull.
For more information on wood ties the Railway Tie Association maintains a comprehensive
website devoted to wood tie research and statistics. Concrete Concrete ties are cheaper and easier to obtain
than timber and better able to carry higher axle-weights and sustain higher speeds. Their
greater weight ensures improved retention of track 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. Concrete ties dampen are
more noisy, so wooden ties are often used in densely populated areas.
On the highest categories of line in the UK pre-stressed concrete ties are the only ones
permitted by Network 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 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 the Hejaz Railway in the Arabian Peninsula, which had an ongoing problem
with Bedouins who would steal wooden ties for campfires.
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 1’s, regional, shortlines, mining, electrified
passenger lines and all manner of industries. Notably, steel ties have proven themselves
over the last few decades to be advantageous in turnouts 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 with track
circuit based train detection and track integrity systems. Without insulation, steel ties may
only be used on lines without block signaling and level crossings or on lines that use other
forms of train detection such as axle counters. Plastic/rubber composite In more recent times, a number of companies
are selling composite railroad ties manufactured from recycled plastic resins, and recycled
rubber. Manufacturers claim a service life comparable with wooden ties, and that the
ties are impervious to rot and insect attack, and can be modified to provide additional
lateral stability while otherwise exhibiting properties similar to their wooden counterparts
in terms of damping impact loads and sound absorption. Dimples can be added on the sides
and bottom the better to grip the 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, and are themselves recyclable. Plastic/Rubber composite ties
are used in other rail applications such as underground mining operations.
In 2009, Network Rail announced that they were to begin replacing wooden ties by recycled
plastic ones made by I-Plas ltd of Halifax, Yorkshire; but the I-Plas went into insolvency
in October 2012. The Cable TV series Factory Made has a segment
on the manufacture of plastic ties. In 2012, New Zealand ordered a trial batch
of “EcoTrax” brand recycled composite sleepers from Axion for use on turnouts and bridges.
Fiberglass Ties may also be made from fiberglass.
Non-conventional tie forms Y-shaped ties 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-sleeper. Noise levels are high but
the resistance to track movement is very good. 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 an I-beam.
As of 2006 less than 1000 km of Y-tie track had been built, of which approximately ninety
percent is in Germany. Twin ties
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. The design is
said to be suitable for track with sharp curves, track subject to temperature stress such as
that operated by trains with eddy brakes, bridges and as transition track between traditional
track and slab track or bridges. Wide ties
Concrete monoblock ties have also been produced in a wider form) such that there is no ballast
between the ties; this wide tie increases lateral resistance and reduces ballast pressure.
The system has been used in Germany where wide ties have also been used in conjunction
with the GETRAC A3 ballastless track systems. Bi-block ties
Bi-block 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 the more flexible steel
connections. This tie type is in common use in France, and are used on the high-speed
TGV lines. Bi-block ties are also used in ballastless track systems.
Frame ties Frame ties comprise both lateral and longitudinal
members in a single monolithic concrete casting. This system is in use in Austria; 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 tie ties are reduced ballast pressure, increased lateral resistance,
and increased support of track. In addition, construction methods used for this type of
track are similar to those used for conventional track.
Ladder track In ladder track the ties are laid parallel
to the rails and are several meters long. The structure is similar to Brunel’s baulk
track; these longitudinal ties can be used with ballast, or with elastomer supports on
a solid non-ballasted support. Fastening rails to railroad ties Various methods exist for fixing the rail
to the railroad tie. Historically spikes gave way to cast iron chairs fixed to the tie,
more recently springs are used to fix the rail to the tie chair.
Other uses In recent years, wooden railroad ties have
also become popular for gardening and landscaping, both in creating retaining walls and raised-bed
gardens, and sometimes for building steps as well. In this case they are often called
railway sleepers and are useful for their solid construction that is built to last.
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 wood preservatives such as coal tar, creosote or
salts of heavy metals, railroad ties introduce an extra element of soil pollution into gardens
and are avoided by many property owners. In the UK, new oak beams of the same size as
standard railroad ties, but not treated with dangerous chemicals, are now available specifically
for garden construction. They are about twice the price of the recycled product. 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 as cribbing for docks and boathouses.
The Spanish artist Agustín Ibarrola has used recycled ties from RENFE in several projects.
In Germany, use of wooden railroad ties as building material 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 the Teerölverordnung, and since 2002 has been regulated by the Chemikalien-Verbotsverordnung,
§1 and Annex, Parts 10 and 17. Ballastless track Ballastless track is designed such that no
underlying ballast is required. The first such tracks were mountain railways with rails
attached directly to the mountain rock. From the late 1960s onwards, German, British, Swiss
and Japanese railroads experimented with alternatives to the traditional railway tie in search of
solutions with higher accuracy and longevity, and lowered maintenance costs.
This gave rise to the ballastless railway track, especially in tunnels, high-speed rail
lines and on lines with high train frequency, which have high stress imposed on trackage.
Paved concrete track has the rail fastened directly to a concrete slab, about half a
meter thick, without ties. A similar but less expensive alternative is to accurately position
concrete ties and then pour a concrete slab between and around them; this method is called
“cast-in precast sleeper track”. These systems offer the advantage of superior
stability and almost complete absence of deformation. Ballastless track systems incur significantly
lower maintenance costs compared to ballasted track. Due to the absence of any ballast,
damage by flying ballast is eliminated, something that occurs at speeds in excess of 250 km/h.
It is also useful for existing railroad tunnels; as slab track is of shallower construction
than ballasted track, it may provide the extra overhead clearances necessary for converting
a line to overhead electrification, or for the passage of larger trains.
Building a slab track is more expensive than building traditional ballasted track, which
has slowed its introduction outside of high-speed rail lines. These layouts are not easy to
modify after they are installed, and the curing time of the concrete makes it difficult to
convert an existing, busy railway line to a ballastless setup.
Slab track can also be significantly louder and cause more vibration than traditional
ballasted track. While this is in some part attributable to slab track’s decreased sound
absorption qualities, a more significant factor is that slab track typically uses softer rail
fasteners to provide vertical compliance similar to ballasted track; these can lead to more
noise, as they permit the rail to vibrate over a greater length.
Where it is critical to reduce noise and vibration, the concrete slab can be supported upon soft
resilient bearings. This configuration, called “floating slab track”, is expensive and requires
more depth or height, but can reduce noise and vibration by around 80%. Alternatively,
the rail can be supported along its length by an elastic material; when combined with
a smaller rail section, this can provide a significant noise reduction over traditional
ballasted track. See also
John Calvin Jureit, inventor of the Gang-Nail metal connector plates
Ladder track Portland cement
Rail tracks Sun kink
Notes References Further reading External links
Die Y-Stahlschwelle in der Schweiz Y sleepers in Switzerland – rack and normal railways.