The challenge is: what do you do when something is moving toward the vehicle's path? You could track every object in front of the car, but since people walk toward the road, then stop, you can't just apply full brakes every time something is moving toward the road.

It's really, really hard to get this right: we humans can look at people standing next to a road, and, based on movement and body language, predict whether pedestrians will walk into a road.

And since there will be cases where pedestrians don't look and walk in front of a vehicle going 40mph, autonomous technology will be limited by the physics of stopping a vehicle with full brake applied.

It's impossible to figure out what the Uber vehicle should have, or could have, done autonomously without looking at the code, and all the data.