I-90 - Four Lakes to Idaho - Operational Study

I-90 Four Lakes To Idaho Locator Map
The study area extends from the Four Lakes/SR 904 Interchange to the Idaho border.


Project background

Interstate 90 (I-90) in the Spokane area, constructed between 1958 and 1974, is increasingly experiencing regular congestion. This congestion occurs primarily during the morning and afternoon peak hours in a commute-directional manner. Non-recurring congestion outside of peak periods is also being seen more frequently. Both of these types of congestion contribute to crashes occurring on this corridor.

The Washington State Department of Transportation (WSDOT), through a programmatic screening process, analyzed highway segments statewide to identify those that have potential for safety improvements. Within the Spokane area, I-90 from the U.S. Route 2 interchange to the Broadway interchange was identified as a high collision corridor segment. Funding for a safety improvement project was received for this section. In consideration of operational performance, the Eastern Region Traffic Office decided to expand the boundaries of the study to encompass the segment from the State Route 904/Four Lakes Interchange to the Idaho State Line, as this is the primary urban core through Spokane.

WSDOT contracted with DKS Associates, an engineering firm, to assist with performing a study focusing on improving safety and operations of the existing freeway through the expanded boundary limits. DKS will examine crash history and operational performance in closer detail and make recommendations for project strategies. This study will emphasize low cost strategies to efficiently move traffic on the existing system in a manner which improves safety and addresses transportation deficiencies, versus higher-cost capacity expansion strategies.

The I-90-Four Lakes to Idaho Stateline Operations Study (pdf 6.3 mb) indicates that crashes have steadily increased over the past five years and are occurring on almost a daily basis. Ramp spacing, weather, and poor driving behavior contribute to the majority of crashes. Likewise, volumes increased by about 10% between 2012 and 2015. This along with the crashes has led to queuing at off-ramps and less reliable travel times, especially in the peak commute hours. The increasing congestion and crashes led to the decision to implement ramp meters through downtown Spokane.  The first ramp meter is scheduled to open April 2019 and will manage the flow of vehicles merging onto eastbound I-90 from U.S. Route 195. 

I-90/Four Lakes to Idaho Operational Study-Final Report (pdf 6.0 mb)
I-90/Four Lakes to Idaho Operational Study-Appendix (pdf 27.5 mb)
I-90/Four Lakes to Idaho Operational Study-Ramp Meter Recommended Operations Handout (pdf 1.3 mb)



Larry Frostad, Assistant Traffic Engineer
WSDOT Eastern Region
2714 N. Mayfair
Spokane, WA 99207