I cannot believe that if a device is “gently tapping” someone’s wrist to call attention to “something important”, the vast majority of drivers will not look at the thing. There are enough distracted morons on the road already, and Apple’s wonderful design quality isn’t going to help.
It’s like looking at your speedometer on your car, or looking at the radio station readout (the FM number or whatever). It’s a glance.
When you drive, you do glances all the time, all around you, inside and outside the car. The key is not having the glance turn into a “preoccupation” ... :-) ...
The Apple Watch avoids it turning into a preoccupation, as would be the case with an iPhone or an iPad.
I have an iPad with me and use Maps with it because the larger screen is great for that. But I have to be careful about looking at that Map when driving. I’ll do a longer glance at it, at red lights, while waiting for the green to come around. In fact in that situation, I’ve actually told my passengers to “tell me when it’s green” ... :-) ...
But the point with an Apple Watch is to make these things unobtrusive, even when you’re in a meeting with people around the table. You can’t make it unobtrusive with an iPhone or an iPad in that situation.