[blake1]

In most modern cars, there is a pressure booster in the power brake system, enabling braking force that can overcome the engine’s horsepower and quickly stop the car. But they are designed to continually maintain the braking force for a limited amount of time—30 seconds or so—after which this boosting ability is depleted. Once that happens, braking must be fully supplied by muscle power via the mechanical backup.

This is challenging if the engine is stuck in a wide open throttle (WOT) state, because the driver must overcome the cars weight in addition to the engine.

For a small car like a Toyota Corolla, this requires a few hundred pounds of downforce on the pedal. For a large 300hp SUV, this could require a thousand pounds of downforce.

As you said, the brakes can bring the car to a stop, but the car will start reaccelerating if the engine isn’t shut off.

(Sorry for mixing physical units.)