520 bridge | 6-lane bridge's cost no easy sell

A six-lane replacement bridge for Highway 520 looks increasingly hard to afford, based on new cost estimates Thursday by the state Department of Transportation.

The new numbers seemingly favor the cheapest of three leading options for an exit to the University of Washington: a larger Montlake interchange plus a second Montlake Boulevard drawbridge, to allow for more traffic and high-occupancy lanes going north and south.

But after more than 10 years of political arguments over bridge design, it's foolish to assume anything.

All three options, each with two car-pool lanes, exceed the $3.9 billion target set by Gov. Christine Gregoire. In January, the governor and state DOT leaders asserted that by accelerating pontoon construction and simplifying design, they could hold costs down.

That's no longer the case.

New features and spikes in material prices boosted costs, said David Dye, deputy DOT director. Some structures, including noise walls, need more concrete and steel than expected.

The design controversies focus on how to design the bridge on the Seattle shoreline. Those choices would result in the following cost for the whole 520 corridor, to Interstate 405:

• The Montlake interchange option, $4.6 billion.

• A high exit bridge over Union Bay to Husky Stadium, $5.1 billion.

• A tunneled exit beneath Montlake Cut, $6.6 billion.

A 34-person mediation group split Thursday over which plan is best.

Seattle City Council President Richard Conlin blasted the cheaper Montlake interchange version. "It will be very difficult for the Seattle City Council to come out in favor of an alternative that offloads freeway traffic onto our neighborhood streets," he said.

The state hopes to open a new bridge by 2016.

The revenue side looks bleak. A total $1.9 billion has been earmarked from state gas taxes, federal bridge grants and other known sources. Only by tolling both the Highway 520 and I-90 floating bridges (which requires lifting a prohibition in state law) could the state raise more than $2 billion and come close to affording the least expensive option.

The state will study all three, look for savings, and consider other funding, said Ron Judd, senior adviser to Gregoire. "Do we do it as an entire project, or do we do it in phases, and how do we pay for that?"