Route diversion (left), from MUTCD Fig 8C-3, Light Rail Transit Signals. Usually in conjunction with or in the same housing as the lowest lens in both two-lens and three-lens signals.
<a href="//commons.wikimedia.org/wiki/User:Mliu92" title="User:Mliu92">Mliu92</a>
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<span class="int-own-work" lang="en">Own work</span>