47 years ago today, 5:04 PM eastern time, the Silver Bridge collapsed taking the lives of 46 people who were stuck in traffic on the bridge. It was ten days before Christmas at rush hour, many of the people who died where commuters.

The bridge was only 39 years old when it collapsed -- and was designed to last for 75 years. The average age for a bridge in New York today is 47 years old.

The bridge was in a fairly good state of repair. However, the bridge was poorly designed, was fracture critical, lacking redundancy in suspension's the eye links, and overloaded with trucks and cars that were much heavier then original design capacity. No technology available in the 1960s could have detected the hairline fracture that had developed and would fail that faithful day.

It was a bridge designed for 1,500 lb Model A's, jammed bumper-to-bumper carrying the large 4,000 lb cars of the 1960s and modern semis much heavier then earlier trucks.

This tragedy lead to national bridge standards, and mandated careful, complete inspections of all bridges at least once every two years, and on older bridges, at least once year. It lead bridge designers to include redundancy in their designs and lead to the end of fracture critical truss bridges for most new designs.