These signs are at a tunnel that goes under Sydney Harbour. I don’t think access to an ample water supply is a major challenge.
It’s also a 3 or 4 year old video, so presumably it’d be easy enough to judge the effectiveness of the virtual signs. I was able to find several articles since 2013 that mention the the tunnels being closed in one direction or the other due to oversized vehicles, but none of them made mention of the virtual stop sign.
