Position of railway not new (3)
I believe the answer is:
lie
'position' is the definition.
(lie is a kind of position)
'railway not new' is the wordplay.
'railway' becomes 'line' (line is a kind of railway).
'not' is a deletion indicator.
'new' becomes 'n'.
'line' with 'n' taken away is 'LIE'.
'of' acts as a link.
(Other definitions for lie that I've seen before include "Fib in alienation" , "Perjure" , "Tell porkies" , "Commit perjury" , "situation" .)