It is run on American lines (7)
I believe the answer is:
railcar
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'run on american lines' is the wordplay.
I cannot quite understand how this works, but
'run' could be 'r' (cricket abbreviation) and 'r' is present in the answer.
'american' could be 'a' (common abbreviation - e.g. in organisation names) and 'a' is present in the answer.
'lines' could be 'l' (abbreviation as in lines of poetry) and 'l' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for railcar that I've seen before include "Powered train unit" , "Small train" , "coach" , "vehicle on the line?" , "form of transport" .)