The most recent report I've seen suggests a plan that would put a temporary "prefab" replacement span in place of the span that failed, with a permanent replacement later. The temporary span would require reduced load and speed for a while, and the permanent fix would just put the bridge back to whatever capacity was being allowed before the breakup.

As to the cost, recent simple highway projects, with concrete just laid on the dirt, have run close to $1,000,000 PER MILE when there are no "complications" to contend with. A recent estimate for a new Texas road ran quite a bit higher because the soil was considered so unstable they'd have to "glue some of it together" before it would hold a slab of concrete so it wouldn't slide out across the prairie when somethin' rolled over it. (And some opinions were they they weren't planning for enough glue.)

As to the truss bridges, later designs in some cases used "multiple redundancy" designs, with a requirement that no single failure would cause anything to fall down. The more sophisticated designs added "only a little" to the cost of the original construction, but less techie methods might easily double the cost. Some afficionados claim to be able to spot the differences "on sight" but it can be difficult even for good bridge engineers to tell without the blueprints and analyses, especially for the more sophisticated "redundant" designs.

Recent reports are that the "official" surveys find something like 66,000 "structurally inadequate" bridges in current use in the US. The news reporters don't seem to think that they need to note where they get their "facts," but the numbers agree with previous reports well enough to be considered "good for talkin' purposes."

SOME OF THESE structurally inadequate bridges have been posted to reduce loads, traffic, and speeds, but others just sit there waiting for someone to fall in the creek. It should be noted that not all of these are "big bridges" and lots of little "local traffic" structures are included in the count. "Classified lists" that show traffic affected by number of "defectives" have been rare.

Counts of "functionally deficient" bridges, as the one in the news was reportedly classified, have not been frequently seen, and none that appear to be as complete as the reports on structurally deficient ones have appeared in any of my sources for some time. The most recent reports have claimed that this bridge has had a number of "incidents" very similar to the recent one, with no visible change in functionality.

Construction of new projects is usually pretty clear cut and the politicians can guess whether to pander to the "fors" or to the "agins." MAINTENANCE is a lot more "iffy," so decisions (and funding) get deferred.

I don't know whether there's a significant difference between the US and elsewhere, but major new projects here quite often include program provisions for funding continued maintenance, but as the maintenance funds accumulate (before the major repairs are needed?) they're seen as a "honeypot" for politicians and frequently get "diverted to something more important." Then when someone disappears into the bottom of a pothole there's "no funds" for the roadway.

John