Central Puget Sound Interstate 5 - Throughput


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Measures of throughput productivity on I-5 in the central Puget Sound region

Throughput productivity

Throughput productivity measures how efficiently existing highway capacity is being used. It can be reported for vehicles or travelers, making it a very adaptive metric. WSDOT uses the maximum throughput standard to assess travel delay relative to a highway's most efficient speed, which is 85% of the posted speed limit. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in decreased throughput productivity.

Lost throughput productivity is the percentage of a highway's vehicle throughput lost due to congestion when compared to the maximum 5-minute weekday flow rate observed at a particular location of the highway for that calendar year. Refer to WSDOT's Handbook for Corridor Capacity Evaluation (PDF 5.9MB) for details on how to calculate throughput productivity.

Sources: WSDOT Transportation Safety and Systems Analysis Division and WSDOT TRACFLOW (https://tracflow.wsdot.wa.gov/)

Note: 100% means a straight line that represents no loss in productivity.

Performance highlights

In 2023, throughput productivity at most locations in both directions of I-5 improved compared to 2022, likely due to the completion of I-5 construction near the Tacoma Dome. After construction was completed, delay in these sections decreased significantly.

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