Many of these works are considered pop art images. This is largely due to the popular styles in retro advertisement prints during these times. Like many pop art images that were used to appeal to consumers, vintage railroad posters are generally representational in nature and often include some form of typography, as seen in the thematic picture, 'Victoria Arduino' by Leonetto Cappiello which is actual meant to be a retro advertisement print for coffee!
Curiously, retro advertisement prints featuring trains were one of the first subjects to employ art deco elements in their work. The symmetry of the train and perspective opportunities of the tracks were highly popular for art deco illustrations. One particular dramatic print that receives this art deco treatment can be seen in the pop art image 'London-Paris Overnight Express' by Steve Forney.
Like all thematic pictures, vintage railroad posters don't only depict trains. These works also depict other kinds of railway interactions, as seen in the vintage railroad poster 'Take Your Dog with You by Rail'. In these thematic prints, it's often the text, rather than the image, which classifies them as a vintage railroad poster.