South Puget Sound Interstate 5 - Severe congestion
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Measures of severe congestion on the I-5 corridor in the south Puget Sound region
Severe congestion
Severe congestion occurs when highway travel speeds are slower than 60% of the posted speed (about 36 mph for a 60 mph speed limit). During this situation, vehicle speeds and spacing decrease along with reduced highway efficiency well below maximum productivity. See WSDOT's how to calculate severe congestion (PDF 5.9MB).
Sources: WSDOT Transportation Safety and Systems Analysis Division and WSDOT TRACFLOW (https://tracflow.wsdot.wa.gov/)
Multi-year trends
In 2022, severe congestion continued to increase compared to 2021 due to the ongoing recovery of traffic volume in the wake of COVID-19. Severe congestion in 2022 got close to the pre-pandemic level.
In 2020, due to the statewide response to COVID-19, there was a significant decrease in severe congestion compared to previous years.
Between 2018 and 2019, nearly every commute on the I-5 corridor in the south Puget Sound region saw an increase in severe congestion throughout the entire day.
Annual highlights
In 2022, severe congestion continued to increase compared to 2021. The congestion level got close to the pre-pandemic level, except for the Lacey to Lakewood and Federal Way to Tacoma commutes, which saw decreaseds in severe congestion compared to 2021. For example, at 4:30 p.m. the Federal Way to Tacoma commute were below 36 mph on 85.7% of weekdays in 2022—a decrease from 93.5% in 2021.
In 2021, most of the commute routes saw an increase in severe congestion conditions compared to 2020, which were still lower than the pre-pandemic levels except Tacoma to Olympia commute. Commuters from Tacoma to Olympia on I-5 traveled less often in severely congested conditions (speeds of 36 mph or less) than in 2020. For example, at 4:45 p.m., speeds on this commute were below 36 mph on 26.7% of weekdays in 2021—a decrease from 34.1% in 2020. Olympia to Tacoma showed an increase in severe congestion in 2021. For example, at 3:55 p.m., speeds on this commute were below 36 mph on 14.7% of weekdays in 2021—an increase from 7.4% in 2020.
In 2020, due to the statewide response to COVID-19 there was significant decrease in severe congestion compared to previous years. Commuters from Tacoma to Olympia on I-5 traveled in severely congested conditions (speeds of 36 mph or less) less often than in 2019. For example, at 4:45 p.m. speeds on this commute were below 36 mph on 34.1% of weekdays in 2020—a decrease from 46.4% in 2019.
In 2019, commuters from Tacoma to Olympia on I-5 traveled in severely congested conditions (speeds of 36 mph or less) slightly more than in 2018. For example, at 4:45 p.m. speeds on this commute were below 36 mph on 46.4% of weekdays in 2019—an increase from 44.0% of weekdays in 2018.
In 2018, commuters from Tacoma to Olympia on I-5 traveled in severely congested conditions (speeds of 36 mph or less) which was similar to 2017.