Driving mode for smart phones

Similar to Airplane Mode, how about Driving Mode?

Something akin to iOS Do Not Disturb, you would set a speed threshold beyond which notifications are silenced - i.e.: >= 25 km/hr, phone effectively silences itself. Slow down again, notifications come back on.

This feature would include the option to explicitly disable Driving Mode if you are, for instance, on a train or in a taxi.

Thoughts?