re: Why don't they build a foot bridge from campus to Northgate?

Don't think a foot bridge would work, back when they had one for crossing the railroad tracks nobody used it, that's why we now have the underpass.

From what I read, it sounds like the two kids jumped the barrier and tried to make it across. They purposely went around a safety feature, so short of making the barrier as tall as the Berlin Wall, not much you could have done to change what happened.