Both Fredericton and Saint John have a similar problem: a rickety old bridge that needs repair. They also both have a walking trail underneath and a liability of concrete falling off the bridge and onto the trail users below. Saint John simply decided to close the trail, which angered a lot of people.  Fredericton on the other hand built this:

A scaffolding cage similar to the kind that you see on sidewalks when they are working on the facades of buildings.  That should hold up to pretty much anything short of the bridge landing on it.

* Keen eyes will also see that the bridge’s catwalk is being held together with old tourism signs featuring the Keddy’s (a defunct local hotel/motel chain) logo.