I've long felt something was off with the Rose Quarter scope and budget, and I've finally put my finger on it. I'm in favor of adding auxiliary lanes and capping the freeway. But ODOT is going about it in the most unnecessarily expensive way possible: They're choosing to build a 250 foot wide cover when a 110 foot wide cover would do.
110 feet is a standard width for a six-lane freeway. It allows for six standard 12-foot lanes, two standard 10 foot outer shoulders, two standard 4 foot inner shoulders, and a 10 foot median. For example, I-5 at Alberta St. is 6 lanes and is 110 feet wide. Capping a 110-foot wide freeway would require two fairly standard 55-foot spans. So why 250 feet? Where does the extra 140 feet of width come from?
First there is ODOT's decision to span the main highway lanes with 75-foot spans rather than 55-foot spans. This is a significant decision with huge cost implications. The required depth of a structural beam is proportional to its length squared, so a girder spanning 75 feet must be 1.86 times deeper than a girder spanning 55 feet. The result is that ODOT is planning to install girders that are about 2 feet deeper than the current girders (which have spans in the 50-60 foot range). This requires lowering the entire freeway by about 2 feet--a hugely expensive project. (see:
https://www.i5rosequarter.org/media/...tion_final.pdf)
So why 75 foot spans when 55 foot spans would do? The obvious answer is that ODOT is building in flexibility to widen the highway to 8 lanes in the future. (Credit to Joe Cortright for being the first to notice the extra width). But ODOT has never admitted that accommodating 8 lanes is part of the project scope, likely because they have no mandate for widening the highway to 8 lanes. Now, there may be a case to be made for building in some flexibility for future possible configurations. BUT: 1) ODOT should actually explicitly make that case to the public and quantify how much it adds to the project budget, and 2) there are ways to accommodate four lanes without blowing up a project budget. For example, 60-foot spans would allow for a possible future configuration with four standard lanes and nonstandard shoulders. Nonstandard shoulders are commonly used to save money in bridges and tunnels. I-93 through Boston, for example, has no shoulders at all. The Marquam Bridge has four lanes and nonstandard shoulders.
The takeaway is this: ODOT is adding hundreds of millions of dollars to the project budget to ensure the provision of standard shoulders in a future lane configuration for which ODOT has no mandate and that
might never be implemented.
What about the extra 100 feet of width? This comes from two 50 foot spans adjacent to the main spans which each cover two exit/entrance lanes. As noted in my previous post, having these lanes split from the highway north of the cover is entirely feasible and would make this extra 100 feet of cover unnecessary. But the ramp locations were set in 2012, prior to the addition of the cover scope. The effect of the ramp locations on the cost of the cover has never (apparently) been considered.
The net result is that ODOT is building a 250-foot wide cover over twelve lanes of traffic when they could be building a 110-foot wide cover over six lanes of traffic. The latter would accomplish the project goal of adding auxiliary lanes, would make lowering the freeway unnecessary, and would massively reduce the cost of the cover.
It's hard to overstate the cumulative effect of these design decisions. They have probably added close to $1B to the project budget. All due to bureaucratic inertia, an inability to reconsider previously made decisions when costs go up, and a questionable (and very expensive) decision made far from the public eye to design for eight lanes instead of six.
I honestly think this should be an Oregonian investigation. $1B is a lot of money.
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