"The ES 350 and most other modern vehicles are equipped with power-assisted brakes, which operate by drawing vacuum power from the engine. But when an engine opens to full throttle, the vacuum drops, and after one or two pumps of the brake pedal the power assist feature disappears.
As a result, a driver would have to apply enormous pressure to the brake pedal to stop the car, and if the throttle was wide open might not be able to stop it at all, safety experts say.
"I don't think you can stop a car going 120 mph and an engine at full throttle without power assist," said Ditlow, the safety center director.
Indeed, a 2007 study by federal highway safety officials showed that braking distance and force on a Lexus ES 350 increased fivefold when the throttle was wide open. And evidence introduced in sudden acceleration trials suggests that it can take up to 225 pounds of pressure on a brake pedal to arrest a runaway vehicle, far more than most drivers can muster from a seated position, said Edgar "Hike" Heiskell, a Charleston, W.Va., attorney who is suing Toyota over a fatal acceleration accident in Flint, Mich.
Lyons acknowledged that the vacuum can be depleted when an engine throttle is wide open, leaving the drivers without power-assisted brakes.
"There's a [federal] standard where you have to be able to stop the car without power-assisted brakes, but obviously I don't think it includes situations where the throttle is wide open," he added.
Drivers in other crashes also found it difficult to rein in a runaway Toyota. Guadalupe Gomez of Redwood City said he was held hostage for 20 miles on a Bay Area freeway by a 2007Camry traveling more than 100 mph.
Gomez was unable to turn off the engine or shift into neutral and then burned out his brakes before slamming into another car and killing that driver, said attorney Louis Franecke, who represented that victim's family."