It's good news that the death count is going to be lower than most people expected at first.
These factors may have been involved:
1. Even though it happened at rush hour, there were far fewer cars than normal on the bridge due to construction. (The strain from the construction equiprment may have been a factor in the collapse, though.)
2. The bridge is partly over water and partly over land, especially on the south side where the railroad tracks run. Many of the cars landed on the land, increasing survival chances.
3. There was quick thinking and good response from some of the victims helping each other and of course the responders who acted efficiently.
4. Minneapolis actually had INVESTED in an 800-Megaherz communication system to be used by emergency responders in situations like this. The investment was very controversial at the time, viewed by legislators of a certain stripe to be "too costly to the taxpayers". While the cell phone systems were failing, this high-tech communication system functioned perfectly and helped save lives.