The index `osm_highway_linestring_highway_idx` is not used. There is also a used partial index `osm_highway_linestring_highway_partial_idx`. I cross check the usage of the index from postgres query stats and all SQL query code where the table `osm_highway_linestring` is refered. This index is relatively big.
transportation
Docs
Read the layer documentation at http://openmaptiles.org/schema#transportation

