Complex sentence: It would eventually be modified for automobile traffic, but traffic was banned in the mid 1970s following an incident when an overweight dump truck caused a portion of the steel grade road on the bridge to break.
Split into simpler sentences: It would eventually be modified for automobile traffic, but is not currently used for that purpose. Automobile traffic was banned in the mid 1970's following an incident when an overweight dump truck caused a portion of the steel grade road on the bridge to break.