Central Puget Sound State Route 520 - Severe congestion
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Measures of severe congestion on the SR 520 corridor in the central 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 Handbook for Corridor Capacity Evaluation (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 since 2021 due to the ongoing recovery of traffic volume in the wake of COVID-19. However, the severe congestion in 2022 was still lower than thepre-pandemic level.
In 2020, due to the statewide response to COVID-19 there was a significant decrease in severe congestion compared to previous years.
All the commutes on the SR 520 corridor in the central Puget Sound region had some amount of severe congestion during both the morning and evening commute peaks yearly from 2018 through 2019. Most of these commutes saw more severe congestion in 2019 than in 2018. The major exception to this was the Seattle-to-Bellevue commute, which saw less congestion during the
morning commute peak in 2019 than in 2018.
Annual highlights
In 2022, severe congestion increased compared to 2021 but was still lower than the pre-pandemic level. Commuters driving from Redmond to Bellevue on SR 520 drove in severely congested conditions (speeds of 36 mph or less), similar to 2021. For example, at 3:45 p.m. speeds on this commute were below 36 mph on 62.5% of weekdays in 2022—similar to 68.8% of weekdays in 2021.
In 2021, severe congestion increased compared to 2020, but was still significantly lower compared to the pre-pandemic level. Commuters driving from Redmond to Bellevue on SR 520 drove in severely congested conditions (speeds of 36 mph or less) more often than in 2020. For example, at 3:45 p.m. speeds on this commute were below 36 mph on 68.8% of weekdays in 2021—up from 28.6% of weekdays in 2020.
In 2020, due to the statewide response to COVID-19 there was significant decrease in severe congestion compared to the previous year. Commuters driving from Redmond to Bellevue on SR 520 drove in severely congested conditions (speeds of 36 mph or less) less often than in 2019. For example, at 7:40 a.m. speeds on this commute were below 36 mph on 7.7% of weekdays in 2020—down from 31.1% of weekdays in 2019.
In 2019, commuters driving from Redmond to Bellevue on SR 520 drove in severely congested conditions (speeds of 36 mph or less) more often than in 2018. For example, at 7:40 a.m. speeds on this commute were below 36 mph on 31.1% of weekdays in 2019—up from 5.8% of weekdays in 2018.
In 2018, commuters driving from Redmond to Bellevue on SR 520 drove in severely congested conditions (speeds of 36 mph or less) more often than in 2017. For example, at 4:20 p.m. speeds on this commute were below 36 mph on 80.8% of weekdays in 2018—up from 74.7% of weekdays in 2017.