When we see reports of unintended acceleration the #1 cause is the driver inadvertently stepping on the throttle instead of the brake and not realizing the error.
In a panic, the last thing they think of doing is pick their foot up, and attempt to hit the brake again. This quite often happens when a driver hits both the gas and the brake at the same time, the throttle will bottom out, well before the brake pedal is fully applied. In a genuine instance of a runaway, the logical thing to do is slip the transmission into neutral, (the heck with the engine, it can be replaced if it over revs) and then turn the key off and pull to the side of the road.
The vehicle in this report uses Toyota's smart key system, and push button start. It is suspected that a misplaced floor mat caused a throttle application and prevented a full brake application. From there, the driver didn't know how to turn the vehicle off, and the car went screaming down the highway at 120mph until the accident occurred. Keep in mind, the driver as a police officer has a lot more experience driving at high speeds than any of us would, and in a pressure situation would likely think clearer than most people, after all that is what he is trained to do. Unfortunately, that was not enough to overcome this situation and as techs when we saw the report, we all realized we would not have known how to shut this thing down either and accomplishing that task would have been more accidental. I may have hit the "start" button, but would not have known to hold it for three seconds. This would have caused the steering lock to apply, but the park mechanism would simply have ratcheted, until the vehicle slowed way down.
Here is a link that might be useful: A very scary tragedy