Railway personifications (鉄道擬人化, tetsudō gijinka) tend to be original character illustrations based on railroad related objects (vehicles, routes, etc.). Some are based on pre-existing works such as Thomas & Friends, Chuggington, and more.
As for the origin of personifications related to railroads, it is not clear exactly what they are.
However, there have been many examples of "characters" that have been portrayed by giving personalities to vehicles, such as Kikansha Yaemon and Thomas the Tank Engine
Thomas the Tank Engine have existed in children's stories for a long time.
In most of these cases, the character is a railroad car with a "face" attached to it.
In November 2006, Densha Gakuen Mohamoha Gumi (unoffical translation) a manga adaptation of personify characters from Tomohito Megumi's website, was serialized for a limited time in the Monthly Dragon Age magazine as his first commercial work.
However, in the majority of cases, most of the personify railroad characters that are the main subject matter on pixiv are fully human characters. This may be due in part to the fact that during the period when personify railroads became established as a genre, vehicle personification, which followed the trend of mecha girls such as MS Girl, took the lead.
The trend is to dress human characters (overwhelmingly female) in clothes designed based on the trains.
Also, night trains and the cars they use tend to have quieter personalities.
Tetsudou Musume does not fall into this genre, as she is not anthropomorphic.
When posting personify railroads, it is preferable to use this tag and related tags as much as possible.
If users who are not searching for personify trains do not disappear after using a negative search, it may be considered as a kind of search obstruction.