"The wagon with opening roof is a type of railway goods wagon that is, nowadays, defined and standardised by the International Union of Railways (UIC) as Class "T". They are a large category of rail vehicle, predominantly used for the transport of hygroscopic bulk commodities such as cement, plaster, lime, potash and grain.
To date, there are four different types of wagon with an opening roof (by way of example, the years refer to when they entered service with the German carrier, DB):
The lidded wagon with several "roof" hatches or lids that can be opened upwards is the oldest type and is rarely seen today. Its disadvantage was that the bars to which the lids were attached meant they could only be opened individually.In 1951 the sliding-roof wagon was built, whereby half the loading area could be opened up and loaded from above without obstruction at one time. This was achieved by sliding one half of the two-part roof over the other.In 1958 came the swing-roof wagon which enabled the entire loading area to be opened up by swinging the roof out on the longer side of the wagon. Its disadvantage is that, in some variants, the opened roof does not fit within the loading gauge and can thus block a neighbouring track.The latest development is the rolling roof wagon that entered service in 1973. Its plastic rolling roof can be completely rolled up at one end enabling the entire wagon to be loaded from above.The overall design and use of these wagons is however governed far more by the configuration of their wagon floors and walls than the methods of loading and unloading. These features, which are also coded by index letters, form the basis of this article´s structure." - (en.wikipedia.org 28.09.2020)
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