Train units (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">train units</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cars that I've seen before include "... when these may be driven?" , "Automobiles" , "Motor vehicles" , "Private vehicles" .)