The basic idea was commercialized by SAFEGE of France: https://en.wikipedia.org/wiki/SAFEGE#SAFEGE_type_monorail https://en.wikipedia.org/wiki/SAFEGE#SAFEGE_typ

The basic idea was commercialized by SAFEGE of France: https://en.wikipedia.org/wiki/SAFEGE#SAFEGE_type_monorail https://en.wikipedia.org/wiki/SAFEGE#SAFEGE_type_monorail However, there just aren't a whole lot of advantages of having a suspended monorail instead of a "regular" straddle monorail. The infrastructure needed is much heavier and bulkier, plus the trains sway rather unpleasantly when turning and if it's windy.