Vertical wooden posts in the street save accident (6)
I believe the answer is:
staves
'vertical wooden posts' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps there's a link between them I don't understand?
'street save accident' is the wordplay.
'street' becomes 'st' (abbreviation).
'save accident' becomes 'aves' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'st'+'aves'='STAVES'
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for staves that I've seen before include "Lines in a music score" , "Barrel pieces; verses" , "Verses. stanzas" , "Slats" , "Lines in a musical score; parts of a barrel" .)