When it was built the traffic estimates were much lower than what we have now. Although having superstructure like that was common then it is not now....for now apparent reasons. Today's bridges tend to be concrete supported from below.

The interstates changed dramatically how goods flowed around the country. Estimates of total traffic expected over fifty years were reached in about fifteen years so these bridges which were intended to last maybe twenty years are now reaching age fifty and still in service.

The bridge was in good repair but was not designed to stay up if one member was knocked out.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.