Don't be shocked if you soon see a left-turn traffic signal on the Spokane Street Viaduct allowing eastbound cars to exit onto Fourth Avenue South.

That's one of the changes West Seattle drivers can expect from Aug. 10 through Aug. 29 to ease the anticipated jam-up of cars seeking ways around nearly three weeks of repairs on the northbound lanes of Interstate 5. A mile-long stretch of I-5 needs to be shored up between Spokane Street and Interstate 90. Only two or three northbound lanes will be open at any given time throughout the repair period.

Traffic signals will be installed on the Spokane Street Viaduct at Fourth Avenue to stop westbound traffic and enable eastbound vehicles to turn left. Some of the viaduct's concrete dividers will be removed so eastbound cars can cross the westbound lanes and take the Fourth Avenue off-ramp.

If the new Fourth Avenue traffic signal works well during the I-5 detours, it might become a permanent fixture on the Spokane Street Viaduct, said Dawn Schellenberg of the Seattle Department of Transportation.

The city is urging drivers to use alternative routes that parallel the section of I-5 being fixed. Fourth Avenue is one alternative. City traffic engineers also recommend using First Avenue, East Marginal Way, Airport Way, Beacon Avenue and Rainier Avenue as substitutes for I-5.

About 90 traffic signals in the Sodo and Beacon Hill areas will have their timing sequences changed to move more cars traveling north and south. East- and westbound traffic in the Sodo area will encounter longer red lights.

Currently signals in the Sodo area are green for 100 seconds. That will be doubled to 200 seconds (more than 3 minutes of green light) for north- and southbound traffic, said Wayne Wentz from the Seattle Department of Transportation.

One northbound lane of Airport Way will be dedicated to buses, trucks and vanpools during the 19 days of I-5 repair work.

"We are really concerned about this particular closure," said Mayor Greg Nickels, who attended a press conference in the city's dimly lighted Traffic Management Control Center in the Seattle Municipal Tower. On a large screen behind the mayor, live video feeds showed traffic conditions at 10 locations around the city.

Traffic engineers can change the timing of specific traffic signals remotely from the center. But none of the traffic signals in West Seattle will be altered during the I-5 repair work because most of the congestion is expected in the Sodo area, Nickels said.

The mayor recommended West Seattleites try the Elliott Bay water taxi to get downtown during the I-5 repair work. He cautioned that many people will be doing the same thing. About 1,000 people are riding the water taxi every day this summer, Nickels said.

Nickels hopes people will use alternative transportation during the I-5 repairs and then permanently change their commuting habits as a result.

The city has more plans for dealing with the expected traffic congestion too.

The Seattle Police Department will assign more officers to traffic duty Aug. 10-29. The city also will have tow trucks on standby to clear away stalled vehicles.

Temporary park-and-ride lots are planned during the I-5 repair work too. The closest one to West Seattle will be at the South Federal Center in the 4700 block of East Marginal Way South.

Residents living south of Seattle who want to go north are urged to hop aboard a Metro bus or a Sound Transit regional express bus.

Better yet, said the mayor, do more work from home and minimize freeway driving. He intends to work from his house in the Admiral District for some of the upcoming days of freeway reconstruction. Nickels also recommended people go to their local cafe to "coffee up, log in and chill out."

Mid-August was selected as the best time to do the I-5 repairs because school is out, many people are out of town on vacation, and the weather is good, explained Nickels.

Late in the press conference, reporters asked Mayor Nickels about other topics, including whether the Seattle Sonics will stay in Seattle.

"There are more important issues in the city," the mayor said, adding as examples, "Education. Transportation."

Tim St. Clair can be contacted at 932-0300 or timstc@robinsonnews.com