[jmillington]

Yes, apparently everything except turning the darn thing off!
According to the report I read, using their loudspeaker, the CHP yelled at the driver to turn the car off, which is how they got the Prius to stop.

"When the Prius, which had reached 90 mph, dropped to about 50 mph, Sikes turned off the engine and coasted to a stop. There was nothing else he could have done to stop the car, Sikes said."