Flat wagon

Flat wagons, as classified by the International Union of Railways, are railway goods wagons that have a flat, usually full-length, deck and little or no superstructure. By contrast, open wagons have high side and end walls and covered goods wagons have a fixed roof and sides. Flat wagons are often designed for the transportation of goods that are not weather-sensitive. Some flat wagons are able to be covered completely by tarpaulins or hoods and are therefore suitable for the transport of weather-sensitive goods. Unlike a "goods wagon with opening roof", the loading area of a flat is entirely open and accessible once the cover is removed.
Flats form a large proportion of goods wagons; for example in 1998 they comprised 40% of the total goods fleet owned by the German carrier, DB, the overwhelming majority of which were flat wagons with bogies.
Typical goods transported by these railway wagons are: vehicles, engines, large pipes, metal beams, wire coils, wire mesh, half-finished steel products,, containers, rails, sleepers and complete sections of railway track. Gravel, sand and other bulk goods are transported on flat wagons with side panels.

International UIC classification

Flat wagons are classified by the UIC into:

Ordinary goods wagons with category letters "K", "O" and "R", and
Special goods wagons with category letters "L" and "S".

The main difference between the ordinary and special types of flat wagon is that the former always have to have a flat deck that can be driven on, whereas the special types do not have to be so designed. Within both types of flat wagon, there are variants with separate axles as well as bogie wagons.
In addition numerous other terms are used to classify flat wagons according to their purpose, but without clear and comprehensive specifications.

UIC standard goods wagons

Attempts by the International Union of Railways to standardise flat wagons go back to the 1950s. These efforts led to the establishment of characteristics for so-called "standard wagons". Standardised flat wagons are specified in the following UIC pamphlets:

UIC 571-1 – Standard wagons – ordinary two-axle wagons
UIC 571-2 – Standard wagons – ordinary bogie wagons
UIC 571-3 – Standard wagons – Special-purpose wagons
UIC 571-4 – Standard wagons – Wagons for combined transport

The implementation of these guidelines is partly binding and partly voluntary for members of the UIC. Since the end of 1977, flat wagons that partially conform to these guidelines are identified by the designation "UIC". Flat beds that comply fully with the leaflets, and are therefore true UIC standard wagons, are given the designation "UIS St".

K: Ordinary two-axle flat wagons

The Class K flats were originally one of the largest families of goods wagons, not least in Germany, thanks to the many older type stake wagons that were assigned to it. The bulk of their work has since been taken over by special flat wagons. By 1998, DB only had 10,000 of this type left.
The majority of ordinary two-axle flat beds built since the 1950s were those with folding sides and short swivelling stanchions of UIC type 1 with, at least in Germany, an axle base of only.
In recent years new K wagons have been developed. These have fixed ends and a tarpaulin cover and are therefore also suitable for hygroscopic goods. Their designation is Kils, based on the UIC classification of goods wagons.
In addition to the normal letters indicating length and weight the Type K may also have the following index letters:

b – with long stanchions
i – with removable cover and non-removable ends and
l – without stanchions
p – without sides
L: Special flat wagons with separate axles

Today this class contains:

Three and four-axle car transporters with one or two decks, and
Two-axle container wagons

Only of historic significance, by contrast, are pod wagons and cradle wagons. As a rule, L wagons do not have stanchions.
The most important index letters for basic classification of current types are:

a – articulated wagon with 3 axles,
aa – double wagon with 4 axles,
d – fitted out for the transport of motor cars without deck,
e – with decks for the transport of motor cars,
g – fitted for the transport of containers.

The UIC has standardised three types of L wagon, the Class Lgss being based heavily on the Class Ks :

O: Mixed open flat wagons

The standard mixed open flat wagon group has folding sides, stanchions and two or three axles.
The most important index letters for this group are:

a – with 3 axles,
k – maximum load <
kk – maximum load
l – without stanchions
m – loading length
mm – loading length <
n – with 2 axles: maximum load >, with 3 axles: maximum load >

The dimensions of the UIC standard wagon largely conform to the considerably more common Class Ks wagon :

	UIC 571-1: Ordinary two-axle wagons
Wagon type	Open/Flat multi-purpose wagon
Class	Os
Axle base
Length over buffers
Loading length, min.
Loading area, about
Loading volume, about
Unladen weight, max.

R: Ordinary flat wagons with bogies

The exclusively four-axle bogie wagons of Class R are equipped with a solid, level deck, usually made of wood, and, unless indicated otherwise by the code letters, also furnished with stanchions and end walls. Most types have short, removable, swivelling stanchions. They are especially suited to the transport of long steel elements, building materials, machines and large vehicles. In the 1990s, the DB purchased Class R wagons with long, sturdy, light metal stanchions and high end walls for the increasing amount of log transport required. In 1998, the DB had about 17,000 R wagons in service.
The most important index letters for distinguishing the basic types are as follows:

e – with drop sides,
g – fitted for the transport of containers,
h – fitted out for the transport of steel coils, eye to side,
i – with removable cover and non-removable ends,
l – without stanchions,
mm – very short loading length,
oo – with non-removable ends, or more in height and without covers.

The UIC has specified two standard R wagons, both of which are very common e.g. in Germany. In the mid-1970s there was a switchover to newly built wagons with foldable sides.

S: Special flat wagons with bogies

This is the largest group of flat wagons both in terms of variety and numbers. Their classification as special wagons arises either as a result of not having a wagon deck that is drivable or due to their axle count. Unlike the standard wagons, these flats are predominantly optimised for a specific purpose. In 1998 the DB had about 22,000 Class S wagons in its fleet.
The large variety of variants may be seen from the number of index letters, of which only the most important are given here; i.e. those that are needed to distinguish the basic types:

a – 6 axles,
aa – 8 or more axles,
d – fitted out for the transport of motor cars,
g – fitted for the transport of containers,
gg – fitted for the transport of containers, total loading length over,
h – for the transport of steel coils, eye to side
i – with removable cover and non-removable ends,
l – without stanchions,
mm – very short loading length,
p – without sides,
r – articulated wagon, three bogies.
S wagons for heavy loads

These wagons are so designed that the loading is limited only by the class of railway line, not the wagon itself. In order to keep the sag as low as possible, they are relatively short and thus mainly inscribed with the index letters mm.
The six-axle wagons with drivable decks of class Samm… are similar to the four-axle Rmm wagons, but are grouped with this special class due to the number of axles. In the Deutsche Bahn, these mainly consist of RRym wagons with a payload.
In considerably larger numbers, and designed for transporting steel coils, are the four and six-axle wagons equipped with loading troughs of the class S…hmm…. Some have fixed end walls and removable covers in the shape of tarpaulins or telescopic hoods. The Shimmns⁷⁰⁸ serving with the DB, which is the most common German S wagon, has an unladen weight of about and a loading limit of and is thus able to carry coils with a total weight of about.
The UIC has standardized a four and a six-axle telescopic hood wagon for the transport of coils. Such wagons have been used in Germany since the 1970s and 1980s respectively, but usually fitted with tarpaulins instead of the hoods:

S wagons for combined transport

The group known as wagons for combined transport have specific designs and equipment for the transport of the various transport units. The UIC has standardized several wagons, whose most important dimensions are given in the following table:

Flat wagons for ISO containers and swap bodies

These wagons of Class Sg… are most common in combined transport. Their foldable trunnions make them suitable for various transport systems. Some of these rail vehicles are equipped with long-stroke shock absorbers as special equipment for the protection of loads.

Wagons with a loading length of at least can carry ISO containers with a total length of ; the majority can also be used for the transport of swap bodies. The Deutsche Bundesbahn expanded its fleet in 2007 by 615 wagons of Class Sgns with the option for a further 600 wagons.
On transporter wagons with a loading length of at least there are an A swap body, up to two C swap bodies or an ISO container with a corresponding total length place.
For the transport of High Cube swap bodies and ISO containers with an inside height of wagons with especially low-lying loading areas and a loading length of have also been available since the 1990s.
Two-part articulated wagons with loading length can be loaded with swap bodies or ISO containers with a total length of .

The use of Kangourou wagon and Wippenwagen remained restricted in the period from the 1960s to the 1980s, despite their utility in enabling horizontal cross-loading without cranes, because at that time facilities for swap body cross-loading were still widely available in western Europe.
The CargoSprinter, conceived as a goods wagon for the transport of ISO containers, did not get any further than trials.