How can I integrate railway embankments to a heightmap?

I would like to create a 16bit PNG heightmap for a PC game, which simulates a real landscape, and I have created a QGIS project.

In this project there is a raster layer for the terrain, which is based on an "*.hgt"-file (30m resolution).

There is also a vector layer that shows the railroad tracks over the landscape. I added this vector layer to the QGIS project using the Quick OSM plug-in (key: railway, value: rail).

I would now like to merge both layers in a heightmap / in a GeoTIFF in such a way that the tracks are integrated on the terrain as slight elevations or depressions – in the same way that they run over railway embankments or in terrain incisions in the real world.

This works probably only if the tracks in the vector layer contain height information – if not, I would like to integrate all tracks as slight increases (1-5 meters) on the terrain, so that railway embankments are automatically generated as part of the heightmap.

How can I implement this?