I'll have to add collapsing overpasses to my list of "things I'd prefer not to encounter while driving". The recent catastrophic failure of part of the overpass near Montreal, Canada, is an illustration of why structural monitoring is your friend.
Signs of Trouble
According to this article from the Syndey Morning Herald, there were earlier signs that not all was well with the structure. One commuter noticed a definite sinking of the roadway and called emergency dispatchers to report it. Earlier reports of concrete falling from the underside were investigated—an inspector sent to the site about half an hour before it fell judged it safe and the roadway remained open, with tragic consequences for the five people killed.
The Laval overpass was inspected last year and passed its inspection. An earlier collapse, of an overpass that was under construction (also in the same region), was later blamed on shoddy construction practices. We won't know for some months why the Laval structure fell down.
From these preliminary reports, however, it appears that although the structure was on the verge of failing, nobody could tell. Here's the problem, or rather one of the problems: if materials internal to a concrete structure start to fail, and there's no external sign of this, you can inspect it until the cows come home, judge it healthy, and then be very surprised when it collapses into a heap of rubble. Yes, non-destructive testing techniques exist to try to assess the internal well-being, and that's important for older bridges, roads, and so on, but for new construction, integrating sensors into the structure itself seems a better way to go.
Applying New Technology to Old Structures
Recognizing that the U.S. infrastructure is in very poor shape, a number of research efforts are under way to enable real-time monitoring of structural health. The ITR Project, a collaboration between academia and industry and funded by the US National Science Foundation, is developing (and testing) strategies to monitor the health of bridges and other civil infrastructure. The project uses a combination of deployed sensor arrays, data analysis, risk analysis, and other methods to try to identify damage based on the changing response of the structure. If you're interested, you can request a Guest registration so you can take a look at the data from the various test beds.