All the school buses near where I live (Sierra Nevada mountains in California) have these - it's cool to watch them lower and start spinning.
But chains aren't enough in some common situations around here that locals, including school bus drivers, know well. When we get a good size snow storm (multiple feet) and the sun comes out a day or two later, thick ice forms on the sections of road that the sun hits - snow melt runs across the road during the day and freezes at night, getting thicker and smoother each day. When that happens on our steeper inclines, chains on AWD/4WD vehicles are not enough to get up those inclines or to stop on the way down them. Locals know where those spots are and take other routes in those situations. It's hard for me to imagine autonomous vehicles having such local information in remote areas like this anytime soon.
But chains aren't enough in some common situations around here that locals, including school bus drivers, know well. When we get a good size snow storm (multiple feet) and the sun comes out a day or two later, thick ice forms on the sections of road that the sun hits - snow melt runs across the road during the day and freezes at night, getting thicker and smoother each day. When that happens on our steeper inclines, chains on AWD/4WD vehicles are not enough to get up those inclines or to stop on the way down them. Locals know where those spots are and take other routes in those situations. It's hard for me to imagine autonomous vehicles having such local information in remote areas like this anytime soon.