I have an enterprise account and they added this button today. Guess what used to be there? The profile image where you could so conveniently swipe up or down to switch between gmail accounts. This is the kind of UI garbage that makes you want to move your entire company to another service just because you can.
But how much do you really know about Driving Mode?
I know enough to drive my car into Google headquarters soon.
For legal reasons that is a joke and I have no intentions of driving my vehicle into the Google buildings.