Central Puget Sound State Route 520 - Delay
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Measures of delay on the SR 520 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 WSDOT's Handbook for Corridor Capacity Evaluation (PDF 5.9 MB).
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 eastbound graph below is read from left to right, while the corresponding westbound graph is read from right to left. For additional details on how to read heat maps, see Handbook for Corridor Capacity Evaluation (PDF 5.9 MB).
Sources: WSDOT Transportation Safety and Systems Analysis Division and WSDOT TRACFLOW (https://tracflow.wsdot.wa.gov/)
Multi-year trends
In 2022, delay continued to increase compared to 2021, due to the ongoing recovery of traffic volume in the wake of COVID-19. However, delay in 2022 was still lower compared to the pre-pandemic level.
In 2020, due to the statewide response to COVID-19 there was no delay in 2020 compared to previous years.
From 2018 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 affordable housing; many of these people commute on SR 520.
Between 2018 and 2019, the SR 520 corridor saw reductions in delay on the SR 520 floating bridge, and increases in delay along the approaches to the I-405 and I-5 interchanges. Delay improvements on the bridge are likely due to the opening of the new SR 520 floating bridge in April 2016. In combination with the Eastside Transit and HOV project (completed in 2015), the new bridge meant that all SR 520 between Bellevue and Montlake Boulevard included two GP lanes and one 3+ HOV lane in each direction. Previously, HOV lanes in both directions ended before reaching the floating bridge and those between the bridge and I-405 were located on the right side of the road, causing congestion due to merging traffic.
Annual highlights
In 2022 delay increased compared to 2021 but it was still lower compared to the pre-pandemic level. The most significant delay in both directions happened at the intersection between SR 520 and Lake Washington Blvd.
In 2021 delay increased compared to 2020, but was still significantly lower compared to the pre-pandemic level. The most significant delay in both directions happened at the intersection between SR 520 and Lake Washington Blvd.
In 2020, due to the statewide response to COVID-19 there was no delay in 2020 compared to the previous year.
In 2019, vehicle delay on SR 520 was very similar to 2017 and 2018. The most notable changes were an increase in eastbound delay on the SR 520 floating bridge during the morning commute, and a decrease in westbound delay on the bridge, also during the morning commute. As in previous years, eastbound delay occurred during the morning commute on the SR 520 floating bridge and approaching 148th Ave. NE, and during the evening commute approaching Redmond. Westbound delay continued to occur during both morning and evening commutes between the I-405 and I-5 interchanges, and was more intense during the evening commute.
In 2018, vehicle delay on SR 520 was similar to 2017. The most notable change was a reduction in eastbound delay approaching the SR 520 floating bridge during the morning commute. As in 2017, eastbound delay occurred during the morning commute on the SR 520 floating bridge and approaching 148th Ave. NE, and during the evening commute approaching Redmond. Westbound continued to occur during both morning and evening commutes between the I-405 and I-5 interchanges.