The infinitely wise Prophet Mohammed (PBUH) advised his followers not to pay more than half of their camels for a dowry, for this could ruin your finances and you'd be unable to provide for your family. Sharia interprets this to mean that women are worth half what men are worth. This means that a woman may not hold more power than a man, so logically Saudi women can't drive.
I don't think that math quite works. I mean, if the man has 100 camels and then gives 50 for his wife, then he now has 50 camels and the wife is 50-camels'-worth. So surely that makes them equal?