An Automatic Train Operation warning sign on the Brooklyn-bound express track at the east end of the 7th Avenue IND Culver station, near Prospect Park under 9th Street and 8th Avenue in Park Slope, Brooklyn. This express track is used as a test track for Communications-Based Train Control (CBTC).
<a href="//commons.wikimedia.org/wiki/User:Tdorante10" title="User:Tdorante10">Tdorante10</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>