Queen, no one minds if you feel that you are upholding your feeling of tznius if YOU dont drive. Its a problem when people say things like “its assur for women to drive” and that is where asking for sources come in.
Honestly, I think you have it backwards. Riding on a bus has the potential to be a lot less tzanua than driving a car. After all, on a bus you could trip (either drawing attention to yourself or having your clothes possibly shift improperly), you could bump into a man, you could sneeze loudly and draw attention to yourself…whereas in a car, the only thing people would see is your head for a moment as you drive by.
Just remember – innate feeling of “right and wrong” are not a Jewish concept. We believe in halacha and that everything stems from the Torah. Going with what you think is “right and wrong” is very dangerous and can lead to you breaking halacha because your thougts were different.