The bridge, as others have pointed out, either would not be there given the glacier flow or would be encased in ice and snow. But assuming it as seen and given how long they have been living in the environment, the travellers would walk along the outside steel structure rather than risking the obviously fragile roadway and in any case would be carrying ropes and using team roping to secure against individual slips & falls when crossing such an obstacle.
In the first scene, where the man and woman are being chased through a tunnel, the man wears a thick down jacket in the first shot. In the second shot he just wears a sweater. In the third shot he wears his jacket again. When they finally reach the door, he is just wearing his sweater again.
In the beginning of the movie a wind turbine is seen with wings having their trailing edge into the wind instead of its leading edge. The wings are either constructed for counter-clockwise rotation (in the movie the turbine rotates clockwise) or are pitched around 180 degrees. Either way, the turning of the turbine is impossible with this blade configuration.
Crazed cannibals or not, the people in the remote site were still human beings with human weaknesses. Being shot in the torso with a .30 rifle round would seriously injure or kill them, regardless of how "psyched up" that they were.
The bridge is shown to have random nearly-circular holes punched through the reinforced concrete on its deck, but almost no damage to its steel superstructure. An ice storm or ice age would not have caused damage like that; nor would any other condition shown in the movie.
Towards the beginning when they cross the bridge there is almost no snow on the bridge. The bridge should be completely frozen and covered in snow, not the clearest and least frozen place they hike through.
If it were indeed cold enough to maintain almost constant snow, ice and cold as well as glaciers, then it would be too cold for the cannibals to travel far in without proper winter gear or head coverings. Hypothermia can set in within 30 minutes and the distance back to The Colony seems to be measured in dozens of miles.
The goof item below may give away important plot points.
The flesh of carnivores (like humans) does not contain as many usable nutrients as that of herbivores, so people who are exclusively cannibals would be weaker than typical; not immensely stronger & faster.