Control of others taking Express? (9)
I believe the answer is:
restraint
'control' is the definition.
(I know that restraint is a type of control)
'others taking express?' is the wordplay.
'others' becomes 'rest' (eg the rest of a group).
'taking' is an insertion indicator.
'express?' becomes 'train' (express is a kind of train).
'rest' enclosing 'train' is 'RESTRAINT'.
'of' is the link.
(Other definitions for restraint that I've seen before include "Moderation" , "Start rain as an impediment" , "It keeps someone or something under control" , "controlling influence" , "Restriction, limit" .)