Bridge Hopper

There are gaps in the bridge (three gaps in levels up to 6, four from there on), but does that deter pedestrians from willfully treading on, like Lemmings or Sleepwalkers, to their demise? Regrettably, that is not the case. Fortunately for the player, a stopgap measure is available to instantaneously block a bridge gap, all at the press of a key, typing in the number of the gap to cover. Unfortunately, as the people cross one gap and approach the next, the makeshift walkway must be moved. If the shameless walkers would cooperate and move in groups, this would be a piece of cake, but instead the player needs to accommodate all of them at their own paces and schedules, regardless of which gap they're approaching. At least they're all traveling in the same direction, right? Well, except for every third level. Wouldn't things be easier if only they'd built the bridge correctly in the first place?