After dark, yes, go anywhere. During the day when people can potentially see you that would be a bad idea. If you can use the vehicle to block line of sight then that could also work.
Right up until a bored small town cop cites you for public urination.
Because... women are never drivers?
They can also go on the side of the road, with the added hassle of disposing of paper. Where do you think they use the bathroom when hiking or camping? And this is why I included cups in my original comment. They can't use bottles as easily on account of the narrow nature, so a cup with a larger mouth is preferred.