Well I did it at about 40MPH. I was looking around for the mode button, when I mistakenly pushed the park button. It went to neutral and some message on the display. I was in a small panic trying to get it back into drive. No damage done. I have pushed it at a very low speed roll and it will go to park. So what is speed it does it do one or the other, I don't know.
up to gen 4, around 6 or 7 miles an hour, but i'd advise against it. they put some buttons in terrible locations.
I did it backing up attempting to close my garage door. It just gave a warning, if you want to perform emergency stop, hold button or something to that extent. I know it didn't stop the car, perhaps it went into neutral.
Previous Prius generations were well protected against damaging user error in mis-selecting Park and Reverse. I'd be quite surprised if Gen4 went backwards on this. Highway speed Reverse and Park attempts produce the same warning and result -- instant Neutral with a double beep warning. I've occasionally practiced shifting to Reverse at highway speed ever since the Sudden Unintended Acceleration scare of 2010, as a faster way to get into Neutral than the delayed shift lever. A reflexive Neutral was one of two things that saved me from damage in a previous car, when extreme fatigue led me to commit a driver-induced SUA while parking. The Prius is our only household vehicle without a manual clutch, so something else is required to disengage the propulsion system.
A traditional automatic shifter is less error prone, both for accidentally choosing Park, or forgetting you're in Reverse?
Perhaps, but then it would possibly preclude auto-park at power-off, which you might consider an important safety feature.
