Central Puget Sound Interstate 405 - Throughput
On this page:
Measures of throughput productivity on the I-405 corridor in the central Puget Sound region.
Throughput productivity
Throughput productivity measures how efficiently existing highway capacity is being used. It can be reported for vehicles or travelers, making it a very adaptive metric. WSDOT uses the maximum throughput standard to assess travel delay relative to a highway's most efficient speed, which is 85% of the posted speed limit.
Lost throughput productivity is the percentage change of highway throughput in respect to maximum throughput due to congestion and other events that cause vehicles to travel below a threshold speed. 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, throughput productivity continued to decrease due to the ongoing recovery of traffic volume in the wake of COVID-19.
In 2020, due to the statewide response to COVID-19 there was less drop in vehicle throughput compared to previous years.
Between 2018 and 2019, three of the four monitored locations on I-405 saw substantial improvements in throughput productivity; the only location which did not see a notable improvement was northbound I-405 at SR 169. The improvements at the other three locations are likely due to the additions of the I-405 Express Toll Lanes in fall, 2015 and the northbound peak use shoulder lane in 2017. For detailed information about the I-405 ETLs, see WSDOT's
I-405 Express Toll Lanes Between Bellevue and Lynnwood | WSDOT (wa.gov)
Annual highlights
In 2022, throughput productivity was worse than 2021, due to the ongoing recovery of traffic volume in the wake of COVID-19. However, throughput productivity in 2022 was still better compared to the pre-pandemic level. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-405 in the central Puget Sound region, WSDOT analyzed vehicle throughput at NE 160th Street and SR 169.
In 2022, vehicle throughput at these locations reached 47% of maximum throughput during their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, slower speeds caused by congestion for commuters traveling southbound at SR 169 at 7:55 a.m. reduced 47% of the freeway's capacity in 2022.
In 2021, throughput productivity was worse than 2020, due to the recovery of traffic volume in the wake of COVID-19. However, throughput productivity in 2021 was still better compared to the pre-pandemic level. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-405 in the central Puget Sound region, WSDOT analyzed vehicle throughput at NE 160th Street and SR 169.
In 2021, vehicle throughput at these locations reached 56% of maximum throughput during their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example,
slower speeds caused by congestion for commuters traveling southbound at SR 169 at 7:55 a.m. reduced 56% of the freeway's capacity in 2021.
In 2020, due to the statewide response to COVID-19 there was less or no drop in vehicle throughput compared to previous years. As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-405 in the central Puget Sound region, WSDOT analyzed vehicle throughput at NE 160th Street and SR 169.
In 2020, there was no lost vehicle throughput productivity at the above locations. Throughput productivity varies by direction of travel, location and time of day. For example, in 2019, 24% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at NE 160th Street at 8:55 a.m.
As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-405 in the central Puget Sound region, WSDOT analyzed vehicle throughput at NE 160th Street and SR 169.
In 2018 and 2019, vehicle throughput at these locations ranged from 38% to 100% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, in 2018 and 2019, 24% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at NE 160th Street at 8:55 a.m. Throughput productivity loss was 20 minutes longer in 2019 than it was in 2018, ending at 9:45 a.m.
As congestion increases and speeds decrease below maximum throughput, highways carry fewer vehicles, resulting in a drop in throughput productivity. To gauge the lost productivity on I-405 in the central Puget Sound region, WSDOT analyzed vehicle throughput at NE 160th Street and SR 169.
In 2017 and 2018, vehicle throughput at these locations ranged from 35% to 100% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, in 2017 and 2018, 23% of the freeway's capacity was reduced due to slower speeds caused by congestion for commuters traveling southbound at NE 160th Street at 8:55 a.m. Throughput productivity loss was 15 minutes shorter in 2018 than it was in 2017, starting at 8 a.m.