"HIGH OZONE TOMORROW" / "CAR POOL"
It's clever in that drivers typically give those signs a lot of credit because they usually warn of lane closures and useful things like that, so in a way it's telling people they should be just as concerned about pollution as they are about safety in construction areas.
At the same time, it seems silly that construction crews would be voicing "Save the Planet!" activist messages like that. Not that I'm against it.. It's just weird to see it on a construction sign. I guess maybe some organization bribed them to do it or something. If that's the case, I hope this isn't the start of a whole era of public service announcements and even paid advertisements on construction signs. People would start ignoring the signs, and that's a bad thing.
Plus, if you think about it, the message is technically flawed. Ozone is a GOOD thing - it's that stuff that blocks out harmful radiation in the upper atmosphere. HOLES in the ozone layer are bad things, and are caused by pollution such as from cars. So, if there's "high ozone", that's hardly anything to be concerned about. Having LOW ozone would be a motive to car pool.