The Quebec Order of Engineers has decided not to blame anyone for the collapse of the de la Concorde overpass in Laval.
Five people died and six were injured when a 65-foot slab of concrete fell onto Autoroute 19 in September 2006.
The order says too much time has elapsed between the overpass's construction and the accident to properly investigate what caused it.
Crucial documents are missing and some of the engineers involved in its construction have passed away.
An Order of Engineers trustee says the structure had to be judged by the standards that were in place when it was built.
He said the eight years since the accident were spent trying to complete the investigation.
A public inquiry report released in 2007 concluded that a so-called "chain of causes" over 35 years led up to the collapse.
It added that negligence in construction and management were ultimately to blame.