Four Lakes to Idaho

  • Home

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 US 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 SR 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 us 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.

What's happening now

The I-90: Four Lakes to Idaho Stateline Operations Study (pdf 548 kb) 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 have increased by about 10% from 2012 to 2015. This along with the crashes has led to queuing at off-ramps and less reliable travel times, especially in the peak commute hours.

Last December, a Study Advisory Group (SAG) was convened and a public open house was held to get feedback on the safety and operational performance of the corridor. This feedback along with findings of the Existing Conditions Report were used to identify areas of high crashes, congestion, and operational performance needs. Targeted objectives were created to address these needs and are documented in the I-90: Goals, Operations Objectives, and Needs Memorandum (pdf 533 kb). A toolbox of over thirty strategies were developed and, using a two-step, Screening Process (pdf 514 kb) reduced to the top six:

A full discussion of the toolbox and screening criteria can be found in the I-90: Four Lakes to Stateline Operations Study Evaluation and Screening Memorandum #4 (pdf 3 mb).


Study information and preliminary data


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