The bumper is designed to rest on straddling a 9mm tie (aka sleeper) between the rails. The dimensions are compatible with the Hume Gauge 1 Railroad track system; the parent project is https://www.printables.com/model/902291-snap-together-gauge-1-model-railroad-track
Print as 2 separate pieces, prototypically in colors of safety orange and red, and then press them together. They are designed for a press fit and glue is not needed.
Print the main body with supports only on the lower undersides. You do not need to support the sloping walls or the horizontal sections near the top.
Orient the bumper part so the plug-in tab is up. Support is not needed.
I have used PETG but PLA would also be feasible.
The author marked this model as their own original creation.