A lot of research has gone into understanding how drunk driving works. Why do people do it? What outside forces influence it? What trends can we find?
One thing that has been discovered is that men tend to drive under the influence far more often than women. Now, clearly the statistics can't take into account every case of intoxicated driving, but looking at arrest statistics and crash data can help to paint the picture. Men appear to be a bigger risk.
Part of the reason for this may be that level of risk itself. After all, one of the main deterrents to drunk driving is just how dangerous it is. People understand the risk that they're taking if they get behind the wheel when they are intoxicated.
It's not that they do not care, per se, but men do tend to take on more risks than women. They'll do things that others think are too dangerous, especially if they think they can "prove themselves" by doing it.
As such, it's not hard to imagine a situation where a young man may agree to drive the group home from the bar when asked, even though he knows that he is probably over the legal limit, because he wants to come across as the helpful hero for the group. A young woman may not care about her social perception as much and refuse to take the same risk.
Of course, drivers of both genders do get arrested for drunk driving in Iowa. All those who find themselves facing charges, no matter how it happened, must know what legal rights they have.