Spokane region Interstate 90 - Throughput
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Measures of throughput productivity on the I-90 corridor in the Spokane 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 how to calculate throughput productivity (PDF 5.9MB).
Sources: WSDOT Transportation Safety and Systems Analysis Division and WSDOT TRACFLOW (https://tracflow.wsdot.wa.gov/)
Multi-year trends
In 2022 similar to 2021, throughput productivity slightly worsened compared to 2020, 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 no drop in vehicle throughput.
Throughput productivity worsened from 2018 to 2019.
To gauge the lost productivity on I-90 in the Spokane region, WSDOT analyzed vehicle throughput at three locations: near Freya Street, Custer Street, and Fancher Road. Several locations on I-90 between Division Street and Argonne Road experienced lost throughput productivity at major chokepoints, such as near eastbound Freya Street, and westbound I-90 near Custer Street and Fancher Road.
Annual highlights
In 2022, throughput productivity was similar to 2021. Vehicle throughput at their congested times was 83% of maximum throughput for these corridors. For example, 17% of the freeway's capacity was unavailable due to congestion traveling eastbound at 5:45 p.m. in 2022 at I-90 at Freya Street.
In 2021, traffic volume recovered significantly from 2020. Vehicle throughput at these locations ranged from 72% to 84% of maximum throughput at their most congested times. For example, 14% of the freeway's capacity was unavailable due to congestion traveling westbound at 7:55 a.m. in 2021 at I-90 near Custer Street. Eastbound evening commute time experienced decrease in throughput productivity but not severe as the pre-pandemic level in part due to the four new eastbound ramp meters.
In 2020, due to the statewide response to COVID-19 there was no drop in vehicle throughput. Vehicle throughput at these locations ranged from 59% to 71% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, 0% of the freeway's capacity was unavailable due to congestion traveling westbound at 9 a.m. in 2020 at I-90 near Custer Street. Throughput productivity loss did not happen in 2020 at I-19 near Custer Street.
In 2019, vehicle throughput at these locations ranged from 67% to 87% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, 33% of the freeway's capacity was unavailable due to congestion traveling westbound at 9 a.m. in 2019 at I-90 near Custer Street. The throughput productivity loss was one hour and five minutes longer in 2019 than it was in 2018, starting at 6:30 a.m. ending at 9:50 a.m.
In 2018, vehicle throughput at these locations ranged from 67% to 87% of maximum throughput at their most congested times. Throughput productivity varies by direction of travel, location and time of day. For example, 33% of the freeway's capacity was unavailable due to congestion traveling westbound at 9 a.m. in 2018 at I-90 near Custer Street. Throughput productivity loss was 10 minutes longer in 2018 than it was in 2017, starting at 6:45 a.m. ending at 9:00 a.m.