I'm assuming that's it moving at a fairly decent clip, and would be able to measure it's rough speed fairly routinely, both actual and from our perspective. If it looks like it's not going to take the better part of an hour or more to pass by I'll stare in awe and concern at it let everyone do the same. Otherwise after minute or two I'll prod everyone back to work, presumably if that things heading to war the bridge's completion is doubly urgent.