I want to make something like in this question in QGIS.
In ArcGIS there is available Make Divided Roads plugin. Is there easy way to make the same job in QGIS?
Related (unanswered) question here: How can I merge/collapse nearby and parallel road lines (eg. a dual-carriageway) into one single line?.
Start with valid singlepart geometries. I'd Buffer at a few different distances that seem appropriate (maybe based on road class too?). Then Dissolve to one buffered road. Now it gets trickier, you need to get centerlines from your polys, see ideas here: Finding centrelines from polygons in QGIS?