Experts appointed by the Metropolitan King County Council said Thursday that a proposal to build a pro sports arena south of downtown creates little risk or economic gain for taxpayers and leaves a few important unanswered questions, particularly around financial and transportation impacts.

Most of the seven volunteer panelists appeared at a council budget-committee meeting to answer questions and expand on papers they wrote for the county, released Wednesday.

"My take-away is that we need to continue looking at economic analysis and transportation, and there are also a lot of positives associated with the proposal as well," said budget committee chairman Joe McDermott.

Council member Bob Ferguson called for an independent analysis that would look at the proposal's impact on economics and jobs in the region. Ferguson wants that analysis to be part of an agreement between the city, county and arena investors led by Chris Hansen.

Through a spokesman, Hansen said he supports Ferguson's idea.

Comments by several panelists were likely to stir controversy and increase demands for more factual analysis of the arena proposal.

In response to the Port of Seattle's claim that a Sodo arena would be a job-killer for maritime commerce, economist Dick Conway said: "If I were the Port of Seattle, the arena is the least of my problems I'd be thinking about." He noted in his report that competition from other ports is increasing.

Port spokeswoman Charla Skaggs said Conway did not talk to Port officials in his research. "Preserving industrial lands and making sure we can operate our facilities efficiently is always a priority because it is key to our ability to compete," Skaggs responded.

University of Washington professor Bill Beyers said more sophisticated research was needed to determine if the Seattle area could support two additional professional sports teams, one in the NBA and one in the NHL.

Conway said Seattle would be the third most saturated sports market in the country based on population and number of teams.

Hansen has provided competing analysis that includes income and other factors and concludes that Seattle is one of the best cities in the country to support new teams.

The group heard sobering comments from retired state Transportation Secretary Doug MacDonald, who predicted an arena sellout would cause a roughly 25 percent increase in car traffic in the central city in early evening.

There are about 17,000 cars an hour between 4 p.m. and 6 p.m. that enter downtown from I-90 and I-5, but only 14,000 between 6 p.m. and 7 p.m. Therefore, if another 4,000 cars head to a basketball or hockey game, the peak congestion would last longer, MacDonald said.

"You could go as high as 180 weekday events, from a present level of 65," he said.

The congestion on most days, and effects on the nearby Port of Seattle, could be absorbed as the price to pay if people want the sports, he said. At least in the case of a single-event day, new construction will help, he said. Elevated Spokane Street is now being widened, and a future Highway 99 interchange will include a freight overpass at Terminal 46. "A lot of the improvements in Sodo make this more manageable than it was a year ago," he said.

But he said conditions are worse in the case of six potential weekday "double days" in a basic year, with both an arena event and a baseball or soccer match. That could be 22 double days if all the Sodo teams make deep playoff runs. The count of ordinary 20,000-fan events would be 65 per year, or 79 in a so-called banner year.

Quoting Charles Dickens' "A Tale of Two Cities," MacDonald said the arena traffic would represent the "best of times" or "worst of times" depending on your passion for sports — or traffic.

MacDonald also noted that the proposal's invitation for thousands of cars to come to Seattle 75 to 100 weekdays a year is an interesting policy position for Mayor Mike McGinn, who for years has campaigned for a greener, less-car dependent transportation system.

University of Washington professor Justin Marlowe, an expert in public-private partnerships, said the arena deal — to build a $490 million arena with up to $200 million in public investment (up to $80 million from the county) that would be repaid over 30 years — carries little or no risk to the county's general fund and bond-rating. Referring to the proposal's safeguards for taxpayers and burden on investors to cover cost overruns and revenue shortfalls, Marlowe said he has not seen "this level of security for taxpayers in any other arrangement of this size."

Still, he acknowledged the deal is not risk-free.

Among the risks, according to other panelists, are the proposal's potential impact on local government taxes, the region's other sports teams, and existing Sodo businesses — all of which warrant further study.

Bob Young: 206-464-2174 or byoung@seattletimes.com

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com