This was purely bad software, and no failure scenario being programmed in. I really don't think it's that difficult to program split-second reaction to obstacles that appear into the driving path. We need to get to a point where these vehicles can do stuff like this, even in a 2-dimensional way:
https://nacto.org/docs/usdg/relationship_between_speed_risk_...
Getting hit at 10mph still is going to suck but it’s a lot more likely to be broken bones and road-rash.
They seem to use 2.5 seconds as the standard for drivers to perceive and react to an obstacle, which based upon studies covers 90% of all drivers. 1.5 seconds to perceive, 1 second to react. Then you have maneuver time on top of that 2.5 seconds.
Given this, 1 second seems very low. A large percentage of drivers would probably plow into them at full speed.
If all but the slowest 10% can react in 2.5 seconds than I would think many would do a fair bit better.
Edit: Apparently the average person is closer to 1.1 seconds. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.372...