Vanishing travelling conditions (5)
I believe the answer is:
going
I believe this clue is a double definition.
'vanishing' is the first definition.
(going is a kind of vanishing)
'travelling conditions' is the second definition.
(the condition of a road or land for travelling)
(Other definitions for going that I've seen before include "Available" , "Departure; current (rate)" , "on the way out" , "attending" , "Ground condition for horse racing" .)