Guided busways (or bus guideways in OSM terminology) are special roadways along which bus operators can travel smoothly at high speeds without steering. These are tagged highway=bus_guideway on OpenStreetMap. Currently, highway=busway is surfaced in OpenMapTiles as the busway class in the transportation layer, but highway=bus_guideway is not present. These two types of roadways serve generally similar purposes, so it would make sense to have guided busways at the same zoom levels.
transportation
Docs
Read the layer documentation at http://openmaptiles.org/schema#transportation

