Why not just put big metal spikes on every climbable surface (other than the drive-way) like stores do with their signs to keep birds away?

Seriously, I'm no architect, but I'm not sure how a barrier is supposed to work - the trained maintenance workers still have to be able to access and climb those parts of the bridge, and if it's simply a barrier with a locked gate to keep out non-employees, a really enterprising person could pick a lock, couldn't they?