Central Puget Sound Interstate 5 - Throughput
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Measures of throughput productivity on the I-5 corridor 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.
Lost throughput productivity is the percentage change of highway throughput in respect to max throughput due to congestion and other events that cause vehicles to travel below a threshold speed. See WSDOT's how to calculate throughput productivity (PDF 5.9MB).
Sources: WSDOT Transportation Safety and Systems Analysis Division and WSDOT TRACFLOW (https://tracflow.wsdot.wa.gov/)
Multi-year trends
Throughput productivity at most monitored locations remained steady between 2020 and 2022.
In 2020, due to the statewide response to COVID-19, there was no drop in vehicle throughput on some of I-5 corridors, while others followed the same intensity as 2018 —2019.
I-5 in the central Puget Sound region, lost throughput productivity occurred at very similar locations and times of day from 2018 through 2019.
Annual highlights
In 2022, throughput productivity at most monitored locations was similar to 2021 while there were minor improvements at other locations. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-5 in the central Puget Sound region, WSDOT analyzed vehicle throughput at three locations: near South 188th Street, near Northeast 103rd Street and at the I-90 interchange.
Throughput productivity varied by direction of travel, location and time of day. In 2022, 20% of the freeway's capacity was reduced due to slower speeds caused by congestion from commuters traveling southbound at South 188th Street at 5:55 p.m. The duration of throughput productivity loss was 35 minutes longer in 2022 than it was in 2021, ending around 6:15 p.m.
In 2021, throughput productivity was similar to 2020. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-5 in the central Puget Sound region, WSDOT analyzed vehicle throughput at three locations: near South 188th Street, near Northeast 103rd Street and at the I-90 interchange.
Throughput productivity varied by direction of travel, location and time of day. In 2021, 19% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at South 188th Street at 5:55 p.m. Duration of throughput productivity loss was almost same time in 2021 as it was in 2020, ending around 6:00 p.m.
In 2020, due to the statewide response to COVID-19, there was no drop in vehicle throughput on some of I-5 corridors, while some others followed the same pattern and intensity as 2019. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-5 in the central Puget Sound region, WSDOT analyzed vehicle throughput at three locations: near South 188th Street, near Northeast 103rd Street and at the I-90 interchange.
In 2019 and 2020, vehicle throughput at these locations ranged from 61% to 84% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, in 2019, 23% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at South 188th Street at 6 p.m. Throughput productivity loss was 55 minutes shorter in 2020 than it was in 2019.
As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-5 in the central Puget Sound region, WSDOT analyzed vehicle throughput at three locations: near South 188th Street, near Northeast 103rd Street and at the I-90 interchange.
In 2019, vehicle throughput at these locations ranged from 61% to 98% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, in 2018 and 2019, 23% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at South 188th Street at 6 p.m. Throughput productivity loss was 10 minutes shorter in 2019 than it was in 2018, ending at 6:20 p.m.
As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-5 in the central Puget Sound region, WSDOT analyzed vehicle throughput at three locations: near South 188th Street, near Northeast 103rd Street and at the I-90 interchange.
In 2018, vehicle throughput at these locations ranged from 61% to 98% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, in 2017 and 2018, 23% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at South 188th Street at 6 p.m. Throughput productivity loss was five minutes longer in 2018 than it was in 2017, ending at 6:30 p.m.