A yellow school bus, its roof visible at the far left of this photo, was one of 100 vehicles crossing the I-35W bridge when it collapsed three years ago.

The book is now closed on one of the worst highway infrastructure accidents in the nation's history. It called into question the state of the country's highways, bridges and overpasses, many of which are more than 60 years old.

URS Corporation of San Francisco announced that the settlement includes no admission of liability or fault, calling the collapse a "tragedy."

The National Transportation Safety Board concluded was caused by a design flaw" and that was "compounded" by subsequent upgrade projects since the bridge was completed in 1967.

NTSB also found that increased traffic, which and construction loads on the day the bridge collapsed into the Mississippi River.

URS was not involved in the original design or building of the bridge, and the planning, design and engineering firm was not involved in any of  the later construction work, including the resurfacing work being done the day of the bridge collapse.

A chartered Type C school bus carrying 52 summer camp students to a swim outing was crossing the bridge when it collapsed at approximately 6:05 a.m. CDT. Nine of the students required hospitalization for their injuries.

The I-35W bridge, a major downtown Minneapolis thoroughfare with an estimated 140,000 vehicles daily, was re-opened on Sept. 18, 2008.