Central Puget Sound Interstate 90 - Delay
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Measures of delay on I-90 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, refer to WSDOT's Handbook for Corridor Capacity Evaluation (PDF 5.9MB).
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, 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
In 2023 westbound delay increased compared to 2022 due to the ongoing recovery of traffic volume in the wake of COVID-19. Westbound delay from Mercer Island to I-5 experienced significant increases in delay. Eastbound delay on I-90 in this region was nearly the same as in 2022, showing almost no delay in traffic.