Was in the driving seat and made straight across lines (5)
I believe the answer is:
ruled
'was in the driving seat and' is the definition.
I can't judge whether this defines the answer.
'straight across lines' is the wordplay.
'straight' becomes 'rued' (I can't explain this - if you can you should believe this answer much more).
'across' is an insertion indicator.
'lines' becomes 'l' (abbreviation as in lines of poetry).
'rued' placed around 'l' is 'RULED'.
'made' acts as a link.
Can you help me to learn more?
(Other definitions for ruled that I've seen before include "with several lines" , "Reigned or ordered" , "Reigned - lined - decided" , "Were tops" , "Governed, used one's authority" .)