Many of the findings in the study, which was commissioned by the Port, directly contradict an earlier study funded by developer Chris Hansen, who wants to build the arena.
Moving freight through the Port of Seattle keeps 17,000 men and woman employed, but road congestion could threaten the port's future.
On Tuesday, port commissioners got a look at just how bad traffic could get if a new arena is built in SoDo.
"What we would like to see is people not gamble with other folks' jobs," said Commissioner Bill Bryant.
According to the new study, freight trucks would have a harder time moving around the added congestion caused by a third sports venue in the area. Street closures around the site would only make that worse, the study says.
Many of the port's concerns aren't addressed in the traffic analysis that Hansen paid for.
"And to date we have seen no actual commitment for mitigation for this arena, and that frightens me," said Marni Heffron, who wrote the new study.
Heffron's company has a long history of working with the port, and she was hired to create a more detailed traffic analysis.
"I think what we have today is a more detailed list of what a real study would look like and the information we need to have before we make any more decisions," Bryant said.
What's missing in both studies is a list of projects that would fix the congestion, as well as what that would cost. Given that, port commissioners voted to ask the Seattle City Council not to commit to Hansen's arena plan until a full-scale environmental impact statement is done.
"Essentially, what you have are people on the city and county council playing poker blindfolded, and the ante is other people's jobs," Bryant said.