I should probably confess that as someone who lives in an area with a lot of construction work, I'm also very vulnerable to "prompt injection" when there's a person standing on the middle of the road holding a sign telling me to change course.
I once encountered an intersection with a big "NO ENTRY" sign on the other side. I turned but google maps wouldn't give me another route, so I did a u-turn and came back to it from the side. Which meant I was close enough to read the small text underneath that said "vehicles under 10 tons excepted". I don't think I've ever been so angry at a road sign.
I came across one in Italy that was meant to prevent you from using a street during school days from X to Y am, and Z to W pm, except on weekends, bank holidays and school holidays.
The idea is well-intentioned, but implementing it by making drivers try to parse arbitrarily complex conditionals while driving is unwise.
There's a sign near my house for a school zone with a reduced speed limit, that used to have conditions similar to the GP's example (though not quite as bad) But they recently attached a yellow light to the top of the sign and changed the condition to "when flashing." That's a much more effective solution.
By my work there is a nice clean sign at the main intersection that reads "NO RIGHT ON RED" with a separate smaller crusty looking sign below it that reads "4 to 5 PM" using a much smaller font. Of course the stark difference in signs means everyone just reads the shiny top sign and waits for the green at all times. I keep wanting to modify the sign to highlight the time.
Obviously. But you can also easily look around at the situation and know when the sign is fake and realize it may be a dangerous situation and disobey. Have you ever seen a green sign that says "Proceed" and just run through a red light because of it? No, you see a construction worker, you see big ass trucks, orange signs and warnings of workers everywhere. If you saw oncoming traffic and people in the road, would you just go because the construction worker flipped his STOP sign around?
Also, I thought we were supposed to make autonomous cars better than humans? What's with the constant excusing of the computer because people suck?