[6][7] However, 81 years later the main span was converted from a swing-type to a vertical-lift type, in order to widen the navigation channel.

The BNSF Railway owns the bridge, and the 5.1 denotes the distance in miles from Portland's Union Station[2] or from the nearby North Bank Depot (or Hoyt Street Depot), which was the Portland terminus of SP&S passenger service coming via this bridge until 1922.

[11] At that time, Portland's Steel, Burnside, Morrison and Madison Street bridges were all swing-type, with center pivot piers seen by boat pilots as inconvenient obstacles.

The Port of Portland organized a committee in January 1906 to determine the feasibility of a bascule-type draw span by inspecting existing bascule bridges in Chicago and other eastern cities.

"[13] After undertaking their inspection, the Port of Portland committee also concluded that a bascule design would be impractical.

[14] The original recommendation for a swing span was ultimately accepted, and plans for the bridge were sent to the Secretary of War for approval in May 1906.

Structural work was completed in July 1908,[1] and the first test swing of the center span was accomplished by a tugboat pushing on it, as the heavy machinery for that purpose had yet to be installed.

[23] Meanwhile, BN and Amtrak trains had to be rerouted via Union Pacific tracks and across the Steel Bridge to reach the west side of the river.

[23] On New Year's Eve 1983, at about 10:25 p.m., two locomotives heading a BN freight train plunged into the river through the open swing span,[25] resulting in the deaths of two crew persons.

[2] That assessment was made by the U.S. Coast Guard, and it led to Congressional approval of a $38 million grant to pay for the work.

[2] Conversion to a vertical lift permitted the central pivot pier to be removed, greatly widening the navigation channel.

In addition to increasing safety, the wider clearance would allow larger ships to reach the Port of Portland's then-new (1978) dry dock facility for ship repair and rebuilding at Swan Island, and Port officials cited both of these benefits in their support of the planned change.

[28][29] After design and engineering were completed, a $28 million contract was awarded in May 1987 to Portland-based Riedel International Inc. to carry out the work.