This is just another way for the city to make money. Not too much different than the speed cameras. They are taking advantage of the tailgating culture and just looking for ways to make more revenue for the city.
The city will make more money when the football team is doing well. But, it will ultimately backfire on them when the football team (God forbid) becomes mediocre or poor again.
No one should ever drive sloppy drunk in the first place, but when you get a whole bunch of people together like at an Iowa football game, that is exactly when you are going to get. The police and the city officials know this and they are looking to get fat off of it.