Bay Area commuters have a reason to rejoice as Washington State has opened its second diverging diamond interchange yesterday. The intersection where Interstate 90 meets State Route 18 near Snoqualmie now features a fresh traffic pattern aimed to significantly improve both flow and safety—offering a promising solution to notorious traffic snarls.
The Washington State Department of Transportation (WSDOT) was to officially launch the new interchange yesterday morning, following an intense eight-day closure required to construct the northern end of the configuration. The innovative design enables drivers on SR 18 to temporarily cross to the left side of the highway while passing beneath I-90 bridges—a maneuver designed to eliminate the need to turn left across oncoming traffic, thereby reducing collision points and smoothing out traffic transitions.
But this isn’t the first rodeo for diverging diamonds in the state. Washington State Department of Transportation opened its inaugural interchange of this type back in 2020 at the I-5/SR 510 (Marvin Way) in Lacey, following in the footsteps of the first-ever such interchange in Springfield, Mo., in 2009. With over 200 such interchanges now spread across the nation, it’s a tried and tested approach to traffic management that holds much promise…