Hello Jarek,

There is a road sign in front of the entrance to the passageway (https://maps.app.goo.gl/QYoxFXcWBGG9fwm9A) indicating whether it's a service road or train operates on it. It is not shown on the image.

Also, according to this wiki page (https://wiki.openstreetmap.org/wiki/Tag:highway%3Dservice) it seems more likely to be a service road. However, recently, I found that highway=service for busways is now deprecated.