I know this is a big task, but could someone give/link me an overview of the state of self-driving cars and the issues they currently face? I know its a hard pr

I know this is a big task, but could someone give/link me an overview of the state of self-driving cars and the issues they currently face? I know its a hard problem but very bright minds have been doing this for a while, so I'd like to know what is the issue, since we've been told for a very long time that the technology is right on the horizon.