Transition lenses are UV sensitive, they will automatically darken once the UV rays hits them when they are exposed to the sunlight. But in your car the lenses won't change the color because your windows have a UV filter and no UV rays can hits the lenses. You still need a pair of prescription sunglasses while driving. If you want prescription sunglasses, I think polarized lenses are much better and clear.
You'd better listen the professional advices not to buy sunglasses with transition lenses. Transition lenses also called photochromic lenses that can adjust to dark lenses when expose to sun while adjust automatically to clear lenses in room. But it takes minutes. Apart from transition lenses, you can wear regular prescription sunglasses that can always in colored lenses and protect the eyes from UV rays in the sun. Or clip on sunglasses is OK.