For the most part, the cost of air raid drills was only time, something which most people waste a lot of anyway (like me, reading LJ, for example). The decision to do a Chicago evacuation drill or not has a number of factors, not the least of which would be how many people would just ignore the drill (look at the number of people who ignore *real* mandatory evacuations because of hurricanes). The most important factor, though, is how many people would die and how much would a drill evacuation cost vs. how many additional people would be saved multiplied by the chance of an evacuation being necessary. Having participated in lots of drills in the military, it often takes a lot of practice to get something right - which means we're not talking just one drill to have a positive effect in evacuating Chicago, but several.
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The decision to do a Chicago evacuation drill or not has a number of factors, not the least of which would be how many people would just ignore the drill (look at the number of people who ignore *real* mandatory evacuations because of hurricanes). The most important factor, though, is how many people would die and how much would a drill evacuation cost vs. how many additional people would be saved multiplied by the chance of an evacuation being necessary. Having participated in lots of drills in the military, it often takes a lot of practice to get something right - which means we're not talking just one drill to have a positive effect in evacuating Chicago, but several.