Immobile excavator losing motorway time (5)
I believe the answer is:
inert
'immobile' is the definition.
(thesaurus)
'excavator losing motorway time' is the wordplay.
'excavator' becomes 'miner' (I've seen this before).
'losing' suggests deleting specific letters.
'motorway' becomes 'm'.
'time' becomes 't'.
'miner' with 'm' removed is 'iner'.
'iner'+'t'='INERT'
(Other definitions for inert that I've seen before include "Not active or reactive" , "Lifeless, without power to move or act" , "Incapable of acting, like some gas" , "Unreacting" , "Torpid" .)