SEATTLE — Officials formally launched a solution to more than 40 years of gummed-up Seattle traffic Wednesday as politicans gathered for a rain-soaked groundbreaking to straighten out the city’s “Mercer Mess.”

U.S. Sen. Patty Murray, who faces a tough challenge in November from Republican Dino Rossi, stood with U.S. Transportation Secretary Ray LaHood, Gov. Chris Gregoire and Rep. Jim McDermott on a four-block stretch that has been leveled for the $161 million project.

The convoluted pattern of one-way streets between the Interstate 5 off-ramps at South Lake Union and Highway 99 are used daily by about 80,000 drivers and pedestrians. The corridor links to the sports and arts venues at the Seattle Center and the neighborhoods north of downtown.