I have never had sunglasses which I was happy with until I got the Sarengeti Rimini with the drivers polar Phd lenses.  These lenses do an excellent job adjusting to the light conditions.  My wife had Transistions lenses several years ago and they would not darken in the car.  It's difficult to tell that the lenses are adjusting while your driving until you turn into a setting sunset.  The first time I experienced that I was amazed.  I'm not squinting or shielding my eyes with my hand anymore.  No more headaches after coming indoors after driving in direct sunlight.  I just ordered another pair of Serengeti's with the 555 Phd lenses.  Can't wait to compare the difference.