But does "autopilot on" mean that "autopilot has exclusive control and driver inputs are ignored"?

No, of course driver inputs will not be ignored. They will override the autopilot. But none were given. From the blog:

>In the moments before the collision, which occurred at 9:27 a.m. on Friday, March 23rd, Autopilot was engaged with the adaptive cruise control follow-distance set to minimum. The driver had received several visual and one audible hands-on warning earlier in the drive and the driver’s hands were not detected on the wheel for six seconds prior to the collision. The driver had about five seconds and 150 meters of unobstructed view of the concrete divider with the crushed crash attenuator, but the vehicle logs show that no action was taken.

> The driver had about five seconds and 150 meters of unobstructed view of the concrete divider with the crushed crash attenuator

So, clearly, the AP is not capable of avoiding such obstacles yet, even when unobstructed. It also seems like a mistake to not slow down to a survivable speed when hands are off...

From the image of the crash site, it looks like the driver was in a spot trying to merge left. That would require you to match the speed of the cars in the other lane. Also it looks like the software made the critical failure of assuming that it was driving in the left lane instead of the shoulder.

https://imgur.com/a/iMY1x

Similar center divide that killed princess Diana.

No, it was a pillar in a tunnel : http://www.washingtonpost.com/wp-srv/inatl/longterm/diana/st...

Perhaps I am just more cautious than most but I always have the follow distance set to give me the maximum separation. That seems to work out at about three seconds. The minimum seems dangerously close to me.