05 owners manual page 133 says if you hold the power button down for 3 seconds or more while driving it will shift to N and go to ACC. If you just push it in for less than 3 seconds I suppose nothing happens but I haven't tried it.
In case anyone is still interested (or not) I tried it today. If you push the power button for less then 3 seconds while driving nothing happens. If you hold it for more than 3 seconds the car shifts to neutral and the hybrid system shuts down, the steering gets a little heavy but its no problem to steer and the brakes still work. After it stops you can select park, hold the brake, push the power button and everything is back to normal.
Just be careful at low speeds if you test that power button functionality. I remember reading a post here or elsewhere describing an owner who pressed Park at 2-3 MPH. At that slow speed, it was said that the Prius would indeed attempt to lock the transmission -- not something I'd recommend anyone do. Since pressing the power button at a standstill would normally engage park, doing so at a low speed might result in a similar behavior rather than neutral. Just a word of warning; most is 3rd-hand information.
i bet if i were having a heart attack, the first thing i would be doing would be braking. B and lifting foot off of accelerator? probably not necessary unless i'm already dead.
the way i see this... his foot is probably on the gas... N will help.. but not that much.. it's a very fast coasting car.. and just for fun, let's say it's on a hill... So.. you're going down hill.. i would hit the power button.. i've done it.. it kinda slows better than N possibly could.. and if his foot is on the gas, B won't help... as soon as i recognize something is wrong (seatbelt of course).. hit the emergency flasher.. hold power button for 3 seconds.. and call 911.. it's hard to turn the car without power assist.. but.. you can do it.. i've done it as a test.. a just in case test.. oh.. btw.. brakes are very difficult too.. hehe.. good luck... hopefully it's not a long hill
