A driving hazard, in two ways (4)
I believe the answer is:
mist
'a driving hazard' is the definition.
(I've seen this in another clue)
'in two ways' is the wordplay.
'two ways' means two replacements for 'way'.
'in' is an insertion indicator.
'way' becomes 'mit' (I can't justify this - if you can you should believe this answer much more).
'way' becomes 's' (Compass direction - South).
'mit' enclosing 's' is 'MIST'.
Can you help me to learn more?
(Other definitions for mist that I've seen before include "Fret" , "Cloud; thin fog" , "low-level cloud" , "Thin layer of fog" , "Mizzle; light rain" .)