The Interstate Bridge Replacement Program

Pictured here is the double truss bridge concept, one of six proposed designs for the replacement for the current Interstate Bridge.

VANCOUVER - The Interstate Bridge Replacement Program released its first batch of visualizations of six replacement bridge options: four single-level bridges, one stacked bridge and one with a lift span.

The renderings have been long-awaited by program critics and supporters alike. The visuals are not a final design and don’t reflect property impacts.

“I almost feel like we should have a drumroll,” said Program Administrator Greg Johnson before the visualizations were shown to the executive steering group at their meeting on Thursday.

Single level

The concrete and steel girder options are similar to one another and resemble the Interstate 205 Bridge.

Although steel might be cheaper in the short term, the cost evens out over time due to having to paint the bridge. Additionally, the amount of fabricators that can do the work is also small, Johnson said.

The ‘extradosed’ and finback single-level options are similar to each other in that the decks are held by a cable—the finback’s are hidden in a concrete container. An extradosed or finback bridge would likely cost slightly more, but not by a significant amount, Johnson said.

On all the single level configurations, light rail will be on the southbound span—next to downtown Vancouver—and the bike-pedestrian path on the northbound span—in the direction of Who Song & Larry’s.

Stacked bridge

Strikingly similar to the final Columbia River Crossing design, a two-level stacked option would put the freeway on the top level and transit and bike-pedestrian paths below.

Because of the limited space between Terminal 1 and the current bridge, a stacked bridge will not be as tight of a fit. One drawback is that the roadway would be higher than on a single-level bridge.

Lift span

Not a part of the original plan, after the Coast Guard requested they study an option with the same or more level of vertical clearance than the current bridge allows, the replacement program is now studying a lift span bridge.

A new lift bridge would be slightly higher than the current I-5 Bridge in order to go over the railroad line—as opposed to under like it does now—however, the amount of bridge lifts will likely stay the same, according to a report published by the replacement program.

The lift span is not a full-fledged alternative, but a design option like the other five options listed.

Johnson said that the reason a bascule bridge — where the roadway opens vertically, like the Burnside Bridge in Portland — is not being studied is because it would be too big and too complex.

Air space requirements

The program is limited in the type of bridge because designers don’t want to protrude into Pearson Field and Portland International Airport’s airspace, Johnson said.

This rules out cable-stayed bridges, like Tilikum Crossing, or suspension bridges, like the Golden Gate Bridge.

Although the Federal Aviation Administration doesn’t have procedural power like other federal agencies — the Coast Guard needs to issue a bridge permit and the federal highway, transit and the U.S. Department of Transportation will decide how much federal grant money to give the program, for example — there are still hurdles.

“If we were to say ‘FAA be damned, we’re going to build a cable-stayed or suspension with towers that extend permanently into their airspace’ the states would incur insurance risk for any incident that may happen,” Johnson said.

With a cable-stayed or suspension bridge, the state department of transportation would need to take out insurance, something they’d prefer to avoid.

“It’s about being a good partner… by doing things that won’t cause the FAA grief,” he added.

Originally published on tdn.com, part of the BLOX Digital Content Exchange.