Blocked motorway going west -- pretty normal (10)
I believe the answer is:
impassable
'blocked' is the definition.
(I've seen this before)
'motorway going west pretty normal' is the wordplay.
'motorway' becomes 'mi' (resembles Mp, English motorway).
'going west' is a reversal indicator.
'pretty normal' becomes 'passable' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'mi' back-to-front is 'im'.
'im'+'passable'='IMPASSABLE'
Can you help me to learn more?
(Other definitions for impassable that I've seen before include "won't be crossed" , "preventing progress" , "Blocked to travel" .)