IF YOU BELIEVE the buzz coming from the auto industry, we're only a couple years away from being able to hail a self-driving car or take a road trip with no one at the wheel. The problem is, experts have been making that prediction for years. The timeline isn't evolving for lack of trying--rolling out autonomous driving technology is just really hard. Here's a breakdown of how it all works and which companies are racing to bring self-driving cars to the masses.