The downtown Seattle bus tunnel will likely be converted to a single use, accommodating Sound Transit's planned light-rail system and not operating as a dual bus and rail line.
A study presented yesterday to the three-county Sound Transit board said that converting the tunnel to dual use could cost $80 million to $163 million, more than three times the original $50 million estimate.
Converting to rail only would cost $33 million to $110 million.
"It just makes more sense for the tunnel to be rail only," said Metropolitan King County Councilman Greg Nickels. The board, which includes suburban mayors and council members from Seattle and King County, will vote on the options in the report in February.
Originally, Sound Transit said the tunnel could accommodate both buses and trains, at least in the first years of operation.
Members showed a greater reluctance to accept a recommendation in the 85-page report to abandon the existing Convention Place Station because the structure is too shallow to handle a rail system, which would be deeper underground.
Several members said after the meeting that they felt it was important to keep a major commuter station at the Washington State Convention and Trade Center, especially because the center is scheduled to undergo a major expansion that will bring in more people and traffic.
"The more likely scenario is to make modifications to the Convention Place Station," said another county councilman, Rob McKenna, who represents the Eastside.
The extra costs for the rail-only system would largely be from building a new station to replace the one at the convention center. The report - done by Sound Transit, Metro and the city of Seattle - outlined an option of building a new station beneath Pine Street. Other costs would include buying new diesel buses since the aging, dual-powered buses (they run on electricity in the tunnel) would no longer be used in the tunnel.
But the costs of converting the tunnel itself to accommodate both buses and light rail would be much higher, as would the cost of continuing to buy the more expensive, dual-powered buses needed inside the tunnel.
Paul Bay, Sound Transit light-rail director, said tracks installed in the tunnel in hopes they eventually would carry a high-speed rail system would have to be torn out and replaced for safety and efficiency's sake because they were installed without the proper rubber insulation needed to operate a modern, electric-powered rail system. The report estimated the cost for that would be up to $110 million. The tunnel was completed eight years ago for $480 million.
Building the $1.8 billion light-rail system also will mean shutting down the tunnel for as long as two years.
And converting the tunnel to light rail only would mean increasing the number of buses above ground by 50 percent, or an extra 188 buses during peak hours through 2006. That could create heavy traffic congestion, and city of Seattle officials would likely have to reroute traffic lanes and create special bus-only lanes along Second, Third and Fourth avenues.
Denny Fleenor, spokesman for Sound Transit, said the changes and costs would not change the overall light-rail project, which is to run from the University District and downtown Seattle to the Seattle-Tacoma International Airport area.