Run down, or even up, motorway to the north (6)
I believe the answer is:
malign
'run down' is the definition.
(I've seen this before)
'even up motorway to the north' is the wordplay.
'even up' becomes 'align' (I've seen this in another clue).
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'to the north' says to put letters next to each other (some letters go above or north of others).
'align' after 'm' is 'MALIGN'.
'or' acts as a link.
(Other definitions for malign that I've seen before include "Laming, showing malice" , "Laming in harmful way" , "Evil, baleful" , "Full of ill will, harmful" , "Evil in nature" .)