[Matt Herring]

Well, this is where the Chevy Volt and like hybrids seek to reverse that way of driving essentially allowing complete expense of the battery before relying on gas. This is more in line with the way people drive their cars...aka...watching the gas guage to know when to fuel up.

The Prius SOC is very fickle and many factors make it go up or down quickly. I've seen my SOC go up by 30% on a heavy downhill when I have to brake for traffic. Just the same, when I was coming out of a nice EV coast my SOC plummeted by about 30% (I only did this because I had a heavy downhill following my coast and knew I was going to be braking and recharging the battery).

But, your example of the failsafe protection of the gas and/or battery engine could take place if someone ran it out of gas on a highway and then ran it out of energy. The car would just die in the middle of the road just like a regular gas engine vehicle.

There are at least 20 threads at priuschat.com about people running out of gas...and then completely draining their battery trying to get to the station or a safer place to park. There seems to be a misconception that the Prius is "magic" and because it has a battery engine it will not die. Unfortunately, this was not the case for many drivers.