"The bilevel car (American English) or double-decker train (British English and Canadian English) is a type of railcar that has two levels of passenger accommodation, as ...
[Read more]
opposed to one, increasing passenger capacity (in example cases of up to 57% per car). In some countries[which?] such vehicles are commonly referred to as dostos, derived from the German Doppelstockwagen.
The use of double-decker carriages, where feasible, can resolve capacity problems on a railway, avoiding other options which have an associated infrastructure cost such as longer trains (which require longer station platforms), more trains per hour (which the signalling or safety requirements may not allow) or adding extra tracks besides the existing line." - (en.wikipedia.org 01.10.2020)