From the Strib (and an email to U of M people yesterday) Safety concerns prompt traffic limits on U bridge
Bikes and Peds will be limited to the center of the upper deck of the Washington Avenue bridge. If the pedestrian weight is a real consideration (as opposed to say, falling off the side, or the need to do reconstruction), that makes me real nervous. The vibration from the trucks and buses below on the lower deck must do more damage than a few dozen pedestrians on the upper deck of the bridge.
It's not like the Golden Gate bridge, where on the 50th anniversary, the bridge flattened out.
I suspect something was not fully revealed in the article.