Congestion on freeways is often caused by collisions, disabled vehicles, or spills that interfere with the normal flow of traffic. With highways in the State of Washington regularly operating at capacity, a blocking incident can result in long backups and extensive delays. Incidents also have the potential for creating secondary incidents as a result of braking and lane changing in the congestion. The Incident Response (IR) program in Washington state is responsible for clearing roadways as quickly and as safely as possible to restore the normal flow of traffic.
The objective of this project is to evaluate the current state of the practice of the IR program in Washington state. This evaluation will include an inventory and comparative analysis of the different program elements. In addition, the project will include an analysis of deployment statistics and service level, to see how incidents are affecting congestion on the roadway. This analysis can be used to develop a needs based system to guide the department on deploying the IR program elements.

The project team has completed a series of analyses that shows the relationship between delays experienced on the freeway and incidents that cause those delays. The amount of delay each incident causes is as much related to when and where the incident happens (because those factors define the amount of traffic present relative to available roadway capacity, and thus the size of any delay likely to form) versus how long that incident lasts.

The results suggest that, in terms of delay reduction, incident response resources have the most benefit when deployed in the middle of the day in heavily congested urban areas, in that quick clearance of incidents at that time may prevent congestion from forming prior to the "normal" onset of peak period congestion. Incident response at other times is still highly beneficial, but the delay savings are not equal to those in the middle of the day. The results also suggest that there are volume points at which incident response is most likely to provide substantial benefits.

The project team needs to confirm and formalize the previous findings. Once that is done, the project team will work with WSDOT staff to determine how to convert the findings into more formal guidance for deployment of WSDOT incident response resources.

Staffing limitations at TRAC have delayed the SHRP2 L03 project upon which the WSDOT project is relying for its analytical results.

WSDOT staff in the NW Region and headquarters have been made aware of potential implementation tasks from this project. They are waiting for more formal documentation to review.