A contract worth $50 million to $150 million awaits an engineering team that can design a replacement for the cracked West Seattle Bridge.

The city on Tuesday issued a request for companies to explain their qualifications and experience to design  a new crossing to serve the corridor’s 125,000 daily travelers.

Engineering teams must prove they’ve delivered at least three government-owned bridges worth at least $200 million each. The winning group would oversee both demolition and construction.

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“Whether we rebuild the bridge would be decided in the next six weeks,” said Heather Marx, director of mobility for the Seattle Department of Transportation (SDOT). “How to replace it would not be decided in the next six weeks.”

The city’s solicitation calls for “a partial or full replacement of the bridge.” SDOT hasn’t estimated a cost, which would depend on how many lanes the city requires, whether the structure includes Sound Transit light-rail tracks and how much money the federal government provides.

While major cracks are concentrated in the 590-foot-long mainspan, that central section is fused by concrete and steel to a pair of sidespans, all supported by columns 122 feet high. The bridge is next to the east-west Seattle Fault, and a new structure must withstand a “2,500-year event” such as the Elliott Bay tsunami of 930.

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The solicitation doesn’t mean the city has given up on repair options, spokesman Ethan Bergerson said.

“It’s all about getting ready to go, so that in the event it has to be rebuilt instead of repaired, we don’t lose time,” he said.

Radar scans are underway, and 75 monitoring devices have been installed to explore structural questions, such as whether internal steel has corroded.

The bridge remains at risk of collapse. The city hired Wisconsin-based Kraemer North America to stabilize the span this year.

The solicitation calls for a potential 10-year contract, in case the city fixes the 1984 bridge, then needs to build a new bridge later, Marx said. But if the city decides to immediately raze and rebuild, she hopes to finish the new route years sooner.

Marx said the city remains willing to take at least a quick look at non-bridge alternatives, such as a shallow immersed-tube tunnel, or a gondola. A 31-member task force of citizens, politicians and business representatives will begin its advisory meetings soon.

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SDOT suddenly closed the 36-year-old bridge March 23, after noticing that seven-year-old shear cracks accelerated by two feet that month. The low-rise Spokane Street swing bridge remains open for freight, buses, emergency responders and longshore workers.

But the lost seven lanes and resulting four-mile detour are already creating congestion and delays at the crossroads of West Marginal Way Southwest and Highland Park Way Southwest, which leads to the First Avenue South bridge.

Traffic on West Marginal has more than doubled, to 26,000 vehicles per weekday.