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Central Puget Sound Interstate 5 Corridor – Delay

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Measures of delay on the I-5 corridor in the central Puget Sound region.

Travel delay

Travel delay is the amount of extra time spent at speeds below a given threshold—such as the posted speed limit or the maximum throughput speed on a highway. WSDOT uses maximum throughput speed (85% of posted speed limit) as its threshold for calculating delay, which it measures in either annual hours of delay per vehicle or annual hours of delay per person. For details on methodology to calculate travel delay, see Handbook for Corridor Capacity Evaluation (pdf 5.9 mb).

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


Heat maps

The heat maps below show vehicle hours of delay by time of day (measured in 5-minute intervals) and milepost. The darker the shading in a particular spot on the heat map, the more hours of delay occurred at that time and place. Shading is standardized across all the corridors to allow for comparison.

There is a separate heat map for each direction of travel. The northbound graph below is read from the bottom to the top, while the corresponding southbound graph is read from the top to the bottom. For additional details on how to read a heat maps, see Handbook for Corridor Capacity Evaluation (pdf 5.9 mb).


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

Multi-year trends

From 2015 through 2019, the central Puget Sound region experienced substantial economic growth and increased employment, which resulted in more commuters on the road. Additionally, rapidly increasing housing prices caused many people to move further from their workplaces in search of housing they could afford; many of these people commute on I-5. Like annual GP person miles traveled, delay on I-5 increased every year from 2015 through 2018, followed by a decrease in 2019.


Annual highlights

In 2019, vehicle delay on I-5 in the central Puget Sound region occurred in the same locations as in 2018, but there was slightly less of it. As in 2018, the most intense vehicle delay on the I-5 corridor occurred northbound between the I-90 interchange and Northgate (including around downtown Seattle), as well as southbound at the SR 520 interchange and SeaTac.

Delay was present on I-5 in the Seattle area in at least one direction for the entire day in 2019, following the same trend from 2018 and 2017. Northbound morning delay was most intense approaching Seattle, while northbound evening delay extended from south of the I-90 interchange to Everett. Delay on the southbound morning commute extended from Everett to just south of the I-90 interchange in Seattle. Southbound delay on I-5 between Northgate and Seattle began at noon in 2019 and continued until 6 p.m., while delay just north of SeaTac lasted from 2-6 p.m., as in previous years.

In 2018, northbound vehicle delay in the general purpose lanes on the I-5 corridor in the central Puget Sound region was similar to 2017, while southbound GP delay was similar overall but concentrated in different locations. As in 2017, the most intense vehicle delay on the I-5 corridor occurred northbound between the I-90 interchange and Northgate (including around downtown Seattle), as well as southbound at the SR 520 interchange and SeaTac.

Delay was present on I-5 in the Seattle area in at least one direction for the entire day in 2018, following the same trend from 2017 and 2016. Northbound morning delay was most intense approaching Seattle, while northbound evening delay extended from south of the I-90 interchange to Everett. Delay on the southbound morning commute extended from Everett to just south of the I-90 interchange in Seattle, but was notably less intense than it was in 2017. As in previous years, southbound evening delay on I-5 was most intense from 2-6 p.m., particularly between Northgate and Seattle, and just north of SeaTac.

In 2017, the worst vehicle delay on the I-5 corridor occurred northbound between the I-90 interchange and Northgate (including around downtown Seattle), as well as southbound at the SR 520 interchange and at SeaTac. Delay was present on I-5 in the Seattle area in at least one direction for the entire day.

Northbound morning delay was most intense approaching Seattle, while northbound evening delay extended from the I-90 interchange to Everett. Delay on the southbound morning commute extended from Everett to south of the I-90 interchange in Seattle. Southbound evening delay was most intense from 2-6 p.m., particularly between Northgate and Seattle, as well as just north of SeaTac.

As in 2015, in 2016 the I-5 corridor in the central Puget Sound region experienced vehicle delay northbound around the I-90 interchange and between Northgate and downtown Seattle, as well as southbound at the SR 520 interchange and SeaTac.

The amount of delay increased significantly in 2016 at certain locations on the I-5 corridor, including: southbound at SeaTac, southbound near the SR 520 interchange, and northbound at the I-90 interchange.

In 2015, the I-5 corridor in the central Puget Sound region experienced vehicle delay in both directions. The most intense northbound delay occurred approaching the I-90 interchange during the morning commute, as well as between downtown Seattle and Northgate. The most intense southbound delay was near the SR 520 interchange and at SeaTac.

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