SR 18 Widening Design

The solution for widening SR 18 consists of two southbound lanes and one northbound lane from Deep Creek to Raging River, and two southbound lanes and two northbound lanes from Raging River to the I-90/SR 18 interchange.

Click and drag the two-way arrow to see how the new solution looks.

Existing condition

SR 18 Widening


  • From the interchange to Raging River, the two southbound lanes include one existing lane and one new lane with a new shoulder.
  • A new two-lane bridge at Raging River accommodates southbound traffic.
  • From Raging River to Deep Creek, two newly built lanes will accommodate southbound traffic.
  • From Deep Creek to Raging River, northbound traffic will continue to be limited to one lane.
  • From Raging River to the interchange, northbound traffic will travel on two lanes. The existing truck climbing lane will be extended to the interchange.
  • Existing fish barrier culverts will be replaced at Deep Creek and Lake Creek, plus additional culverts as necessary.


  • Reduced impacts to wetlands and streams along the corridor.
  • Wider shoulders.
  • Median barrier between Deep Creek and SE 104th St.
  • Roadway designed to accommodate 55 mph speeds.
  • Traffic models show up to a 12% reduction in total crashes and a 15% reduction in fatal and injury crashes compared to not widening SR 18 from Deep Creek to the interchange.
  • Traffic models show significant improvements in travel times in 2045 for both morning and afternoon peak travel periods, and in both directions, over not widening SR 18 from Deep Creek to the interchange.