This tragedy shows the importance of inspection and cost of maintenance of infrastructure. In the U.S. there are approximately 600,000 highway bridges. It's estimated that a quarter of them are at their end-of-life mark (that avg being estimated by some at 70). Not counting over 1,700 bridges still in use built before the 19th century, the breakdown is something like this:<p><pre><code> Decade No. Built
1900 6,084
1910 5,893
1920 17,883
1930 42,009
1940 25,971
1950 64,085
1960 99,975
1970 82,129
1980 78,279
1990 81,410
2000 71,475
2010 38,038
</code></pre>
This is just bridges. There are also about 84,000 dams and in a decade or two a huge number of both of these will approach their end of life, just as a legion of civil engineers go into retirement.