From an LA Times article:
One obvious line of defense is to simply shut off the engine, a step that may not be intuitive on the ES 350. The car has a push-button start system, activated by the combination of a wireless electronic fob carried by the driver and a button on the dashboard.
But once the vehicle is moving, the engine will not shut off unless the button is held down for a full three seconds -- a period of time in which Saylor's car would have traveled 528 feet. A driver may push the button repeatedly, not knowing it requires a three-second hold.
"When you are dealing with an emergency, you can't wait three seconds for the car to respond at 120 miles an hour," said Clarence Ditlow, executive director of the nonprofit Center for Auto Safety.
The ES 350 Saylor was driving that day was a loaner provided to him by Bob Baker Lexus when he took his family's Lexus in for servicing. It's unclear whether Saylor's own car had the same feature or whether he was aware of the shutdown procedure. Bob Baker Lexus did not return calls.