The replacement of the 520 bridge debate has been going on for 20 years now, and is making progress, albeit slowly. I can't recreate the gist of that entire debate, complete with engineering and cost data, in a short post, so if you aren't familiar with these issues, this will be hard to understand. If you are somewhat familiar with the debate and wish to understand further, check out the quality project documentation on the Washington DOT site. (A quick aside for those outside of Washington State - if you've ever seen a Husky Football game televised the bridge in the background of the Stadium long shots is 520.)
Seattle Mayor Mike McGinn has added a the transit requirement as a political calculus adding the pro-transit folks to the option K/Montlake Cut Tunnel folks, but the proposal is not faring well among the long term stakeholders. This has proven controversial in early reports.
I believe I was the first to bring up the option K concept, in 1988, but it may well prove too expensive. I will still defend option K, including as modified by Mayor McGinn, so long as the lane is joint use for both bus and light rail transit, and, perhaps, intelligently equipped public safety vehicles).
At this point there are two paths to proceed along with this public design, tweak the option A+/L (L is a bridge version of K, and might be the best compromise) range of options to improve transit function and reduce impacts on Montlake OR continue to look at option K in a larger context.
As a minor point, please note that transit improvements to the currently winning alternative, A+, will marginally increase the cost, perhaps as high as the option 'L" budget.
The reality of Montlake being able to delay the project still, is a political reality. This would give the time to look at the transit network options in further refining option K. For example, why not drop that third transit lane from the Montlake to I5 segment and enhance transit connectivity from Montlake to Capitol Hill (and Downtown) as well as Montlake to the University District (and I5)!
Removing the third lane from the Montlake to interstate 5 segment is also an alternative, and could further reduce the costs of the current preferred version.
