I have recently been down this path. I needed to get prescription glasses as my vision had deteriorated to a point where just reading glasses did not cut it anymore.
Transitions now makes a type of lens that they call
Transitions Drivewear | Driving Sunglasses
Driveware does get darker when you are inside a car. But, they never get fully clear. They always have a noticeable tint. Also, these lenses are limited in regard to who carries them. It looks like Wal-Mart optical centers carry them, but there are none of those near me.
In the end, I decided to go with regular prescription glasses and prescription sunglasses. However, as noted by many above, it is a pain carrying around two pair of glasses. If I needed to do it again, I would go with normal Transitions lenses for my everyday, walk-around glasses and get a pair of prescription sunglasses to keep in the car.