I would like to know what is the difference between "fast" and "short" on the route conditions in the nav menu? The reason I ask is because I stay in Milwaukee, WI and I traveled to Chicago, IL and I calculated my route and as I was on the highway several times it prompt me to get off the highway and take the street. What I did was disregard her commands and continue to proceed on the highway to my destination, but still she kept asking me to get off and take the street. Keep in mind the drive was about 1hr 30min long on the highway, so image how long it would be on the street even if there is a street that takes you that way. So once again my question is, what is the difference between "fast" and "short" on the route conditions in the nav menu?

Fastest takes into account the speed limit of the roads and the distance traveled on those roads. So the route may be longer but the speed limit could be higher and the AVIC would think that you would arrive sooner. For this to work properly you must set the average speeds to what you would typically drive on that road.

Shortest takes into account the driving distance only.

There are also areas you can set it to avoid; freeways, ferries, tolls.