The only system for avoiding head-on collision? (3-3)
I believe the answer is:
one-way
'avoiding head-on collision?' is the definition.
I can't tell whether this defines the answer.
'the only system' is the wordplay.
'the only' becomes 'one' (I've seen this in another clue).
'system' becomes 'way' (I am not sure about this - if you are sure you should believe this answer much more).
'one'+'way'='ONE-WAY'
'for' is the link.
Can you help me to learn more?
(Other definitions for one-way that I've seen before include "Not allowing reverse motion" , "Allowing travel in one direction only" , "Allowing movement in one direction only" , "Street allowing traffic in single direction only" , "Allowing no return movement" .)