Seattle and King County are suggesting several road improvements in Sodo, mostly for freight trucks, to address the Port of Seattle's objections to a proposed sports arena.

No specific ideas for funding the 13 projects, worth roughly $25 million, were included in the letter, sent to the Port on Tuesday by staffers representing Mayor Mike McGinn and County Executive Dow Constantine. Both are arena supporters.

The cost and responsibilities would be shared by the three governments, said Tim Ceis, a former Seattle deputy mayor who is now a consultant to the Seattle Department of Transportation for arena and Sodo issues.

Ceis said the arena sparked weeks of discussions of how to make better use of roads and rail. The city and county issued the letter in hopes of getting a formal response from the Port, he said.

"We appreciate the letter. This is just right out of the gate," said Port spokesman Peter McGraw. Gael Tarleton, Port commission chairwoman, hadn't received a copy yet.

The two biggest proposals are a new truck road directly into the Argo rail yard, taking trucks away from Highway 99 south of Spokane Street, at a cost of up to $10 million; and a traffic-information network, with electronic signs to send drivers to less-clogged routes near stadiums, for up to $15 million.

The Port has pushed back hard against the proposed 18,500-seat arena just south of Safeco and CenturyLink fields. The additional traffic for pro basketball and hockey would interfere with trucks near the waterfront, the Port says.

McGinn believes the city's share would be affordable without new voter-approved taxes, spokesman Aaron Pickus said. Sung Yang, Constantine's chief of staff, said officials could seek state or federal grants.

Some projects have been on the drawing board for years, as the Port competes with rivals on the Pacific and Gulf coasts, and hopes to boost container shipping by more than half by 2030.

The projects include:

• Lane extensions to the new East Marginal Way South overpass, which flies over train tracks near South Spokane Street;

• Restricted access on East Marginal Way at the waterfront.

• A left-turn lane to Terminal 30, to favor trucks;

• A "heavy haul" route, paved to handle overweight loads;

• Terminal 18 entrance improvements on Harbor Island;

• Better signs near the lower West Seattle Bridge;

• Lanes for trucks waiting to enter port gates;

• Access to cruise-ship docks;

• Expansion of the "E-Park" system showing where space is available;

• Change road layouts to reduce truck-bicycle conflicts;

• Provide overnight parking spaces for trucks.

The arena presents two other kinds of transportation challenges. Safer rail crossings and sidewalks are needed for sports fans to reach their cars and transit. And arena traffic would add more nights of congestion to the I-5/I-90 junction.

City officials have said arena investor Chris Hansen's team would fund pedestrian facilities on South Holgate Street. Regional traffic is an open question — and it would be aggravated if drivers avoid future Highway 99 tunnel tolls.

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