An illustration of how the MTA styles "subway" and "subway system" in lowercase at the bottom of <a rel="nofollow" class="external free" href="https://new.mta.info/guides/riding-the-subway">https://new.mta.info/guides/riding-the-subway</a> -- snips of their text as rendered and blurred by me.
<a href="//commons.wikimedia.org/wiki/User:Dicklyon" class="mw-redirect" title="User:Dicklyon">Dicklyon</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>