Lacking will to use US highway, cutting out middle of journey (9)
I believe the answer is:
intestate
'lacking will' is the definition.
'cutting out middle of journey' is the wordplay.
'cutting out' becomes 'cutting off' ('cut off' can be a synonym of 'cut out').
'middle' means to look at the middle letters.
'of journey' becomes 'testate' (I can't explain this - if you can you should give a lot more credence to this answer).
The central letters of 'cuttingoff' are 'in'.
'in'+'testate'='INTESTATE'
'to use us highway' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for intestate that I've seen before include "Unwilling" , "Not having planned to leave" , "Not having written a will before death" , "Dying without having made a will" , "Lacking a will" .)