MUTCD R5-1 as it appears in MUTCD 1961. Due to the low quality of this work (scanned physical copy of 1961 MUTCD), it is not recommended for use in articles
<a href="//commons.wikimedia.org/wiki/User:Dangeredwolf" title="User:Dangeredwolf">Dangeredwolf</a>
2019-02-28
<span class="int-own-work" lang="en">Own work</span>