Streetcar tracks (9)
I believe the answer is:
tramlines
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">streetcar tracks</span>' is the definition.<br/ ><span class="explanation-format__explanation">('tramline' can be a synonym of 'streetcar track')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tramlines that I've seen before include "rigid principles" , "Tracks" , "Side markings of tennis court" .)