One of the most amazing things about this would be to remove signs altogether. Just embed the sensor in the pavement and give the space the signs took up back to people, nature, or literally anything else.
Huge overhead highway gantries and traffic lights would be wonderful to remove, too. City sidewalks are narrow enough as is and they would be way better without 20+ft tall metal poles jutting out of the ground. Hopefully we can put trees in their place, but maybe I’m dreaming.
I forget where I read this, but someone posited that the goal has always been “all day” battery. Ever since the first smartphones ,we’ve had, largely, the same battery life. It lasts most of the day and that’s good enough for most people. The secret, though, is that actually the batteries have gotten way bigger and more energy dense, it’s just that the processors and mobile radios are also more power intensive.
I suspect if you put a modern battery in a 5 yr old smartphone it would last 2+ days. But you’d have to deal with 3G radios, bad GPS, and slow performance.