According to this article, it says:I've read that all 2016 cars have to have them.
"The rule -- which would be final in 60 days -- would start phasing in on May 1, 2016 models and be at 100% May 1, 2018."
But that's for all "New" cars and trucks; doesn't address older cars and that's the majority of vehicles on the road.
The one part in the article that I just shook my head at "two parents that had backed over their own children, were suing the Obama Administration"
That goes to show what a sue happy society we live in, and how people refuse to take responsibility for their own actions.
Even when they have cameras installed, the driver still has to be observant enough and use them!