NY submitted this idea :
Am I right that the last thing you want to do is let the engine greatly
exceed its redline speed and risk it seizing up (I'm assuming that the car
is old enough not to have a rev-limiter)? Do any steering locks actually
lock the steering while the key is still in, even in the off position? I
thought it only locked when the key was removed - for this very reason, so
you can safely turn off the engine in the event of an emergency.

A modern engine under ecu control will not exceed the redline, unless
there is some outside influence.

The outside influence being either going down a very steep hill and
heavily laden, or a diesel engine which has begun running out of
control on its sump oil. Ignition switched to accessory (I) should work
to kill the power from the engine, apart from a run away diesel. Hard
on the footbrake should slow the car plus engine down.

If in the case of a run away diesel engine you cannot slow down enough,
clutch down, into neutral brake and let the engine self destruct.