How many more bridges?

I think that's a fair question after the tragedy in Minneapolis yesterday. The great bulk of highway construction in North America happened some 40 or 50 years ago and I think it's fair to start wondering about the lifespans of the great bulk of these aging structures. Are we putting enough money into inspecting and maintaining our roads? Politicians of every stripe love the appeal of cutting a ribbon for anything new (a bridge, a highway, a terminal at an airport), but I wonder how the various jurisdictions in North America are doing when it comes to boring old inspection and maintenance.