A major road closure is set to affect SR 18 near Snoqualmie for five days, starting at 9 p.m. on May 15 and ending on May 21, according to the Washington State Department of Transportation (WSDOT).

The plan: This closure is necessary for building the southern end of a new diverging diamond interchange.

• The interchange aims to make traffic flow smoother and safer by reducing the crossing paths of left-turning vehicles.

Detour details: Freight traffic will need to follow a specific route to bypass the closure.

• Truckers can use I-90 and loop around at the Preston-Fall City (exit 22) and Southeast North Bend Way (exit 27) interchanges.
• It's important not to use Issaquah city streets or Issaquah-Hobart Road; these aren't suitable for semi-trucks.

How it works: Diverging diamond interchanges allow vehicles to turn left onto freeway ramps without crossing opposing traffic, increasing efficiency and safety.

The big picture: Over 150 of these designs exist across the U.S., reported WSDOT.

Commuters should plan for delays, but I-90 itself will remain open.