Most people are pretty oblivious when it comes to knowing how much UV protection their car windows provide. They mistakenly think that their blueish or greenish glass protects them from sun damage while driving. In the USA, automotive glass must meet specific federal requirements pertaining to how much light can pass through the windows. But there are no such standards in terms of requiring them to provide sun protection from UV rays.
So is it safe to say that you are a sitting duck to skin cancer when you are driving? Actually yes but no. Out all our your windows in your car, the windshield glass usually provides the most sun protection and your sunroof / moonroof may block up to 90% of UV rays surprisingly. But it is still recommended for everyone to apply SPF 30+ broad spectrum sunscreen before heading out in your automobile.
Maybe if we can get enough people to petition their local congressman to write a bill that will mandate all automobile glass manufacturers to include 99% UV blocking material into all car windows, it will make a big dent in fighting our war with skin cancer!