Central Puget Sound State Route 520 - Severe congestion
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Measures of severe congestion on SR 520 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) leading to reduced highway efficiency. Refer to 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/)
Performance highlights
Severe congestion in 2023 increased slightly compared to 2022 and was close to reaching pre-pandemic levels. In 2023, commuters driving from Redmond to Bellevue on SR 520 experienced more severe congestion (speeds of 36 mph or less) than in 2022. For example:
- At 3:55 p.m., travelers experienced severe congestion on 79.8% of weekdays in 2023 an increase from 62.5% in 2022
During the peak evening commute from Bellevue to Seattle:
- At 8:35 a.m., travelers experienced severe congestion on 58.0% of weekdays in 2023 compared to 22.3% in 2022
- At 3:40 p.m., travelers experienced severe congestion on 93.4% of weekdays in 2023 compared to 74.1% in 2022
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.