^ What kind of experience have you had with a polarizing filter? I have read on the internet, that for the best results with a polarizing filter should be adjusted based on the varying light levels of the day. Do you just leave the same filter on your lens all the time?
If it's anything other than midday, you pretty much have to rotate it when you change direction. It also depends on how harsh the light is, or the angle of the sun. Sometimes you need to move it about an equal number of degrees as you've turned the vehicle. Other times, half as many degrees for each turn. It varies. And there's times I mess it all up and you have 100-200 photos which were too dark or still had too much glare, although an SLR will essentially give you the WYSIWYG effect unless you ignore over/under-exposure warnings.
You might not need one if you're directly opposite from a setting/rising sun, or if it's very cloudy.
Obviously, this isn't practical on a winding road, but about a quarter-turn for each 90 degrees of directional change does the trick. It's tempting to totally darken the skies, but at the expense of losing most detail below the horizon. It's also possible to darken the skies so much that glare on the bottom-third of the windshield re-appears, so you have to find a happy medium.
There's also the annoyance of too much brightwork on automotive interior trim; I sometimes wonder if a few interior automotive designers have actually driven a car on a sunny day before.