Spokane region Interstate 90 - Throughput
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Measures of throughput productivity I-90 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. Refer to 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/)
Performance highlights
In 2023, throughput productivity was similar to 2022. Vehicle throughput at the most congested times was 77% of maximum throughput for these corridors, meaning that 23% of the freeway's capacity was unavailable due to congestion traveling eastbound at 5:50 p.m. on I-90 at Freya Street in 2023.
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, 15% of the freeway's capacity was unavailable due to congestion traveling westbound at 5:35 p.m. in 2021 at I-90 near Freya 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. 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.
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, 18% of the freeway's capacity was unavailable due to congestion traveling westbound at 5:50 p.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 3:25 p.m. ending at 5:55 p.m.