Troublesome inertia on sides of railway route (9)
I believe the answer is:
itinerary
'route' is the definition.
(I know that route can be written as itinerary)
'troublesome inertia on sides of railway' is the wordplay.
'troublesome' is an anagram indicator.
'on sides of' says to hollow out the word (remove centre letters).
'railway' with its centre removed is 'ry'.
'inertia' anagrammed gives 'itinera'.
'itinera'+'ry'='ITINERARY'
(Other definitions for itinerary that I've seen before include "schedule" , "Plan of a journey, route" , "Planned journey" , "List of places" , "Record of a journey" .)