Queue of traffic (8)
I believe the answer is:
tailback
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">queue of traffic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tailback that I've seen before include "Long queue of traffic" , "Lack a bit (anag.)" , "Queue of cars" , "delayed traffic" , "Traffic hold-up" .)