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Scoping Bottlenecks [Iowa]

Iowa Department of Transportation · 2025 Full Details

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Title
Scoping Bottlenecks [Iowa]
Description
Several layers were examined as part of the highway improvement needs analysis conducted for the latest long range plans. Needs aligned with highway traffic and freight bottlenecks identified in the latest State Long Range Transportation Plan (SLRTP) and Freight Plan. A combination of INRIX travel time data and input from internal and external stakeholders was used to identify bottleneck locations.Locations on the Primary Highway System that had recurring slow-downs, or bottlenecks. INRIX travel speed data, derived from cellphone and global positioning systems data, was used to identify bottlenecks. Bottleneck conditions were determined by comparing reported speeds to reference speeds for each segment of road. Reference speed values are provided for each segment and represent the 85th percentile observed speed for all time periods, with a maximum value of 65 miles per hour (mph). A bottleneck occurence is defined in this analysis as a time interval where the average traffic speed is less than or equal to 60 percent of the reference speed. The annual total bottleneck duration per mile was calculated for each segment to represent recurring congestion, and the worst five percent of the overall network was identified. Of those locations among the worst five percent by duration per mile, locations where the duration was one standard deviation or hight than the statewide average were identified as bottlenecks for the SLRTP. Some of these bottlenecks are on the Iowa Multimodal Freight Network and of particular concern for freight traffic. These bottlenecks are further analyzed in the State Freight Plan, which prioritizes them based not only on amount of delay but also on conditio nand value for network efficiency.For more information, see https://iowadot.gov/iowainmotion/.Note: this dataset supersedes SCOPING_FREIGHT_RETIRED, effective with the publication of the State Long Range Transportation Plan (SLRTP) and Freight Plan update in 2022. In previous long range planning updates, bottlenecks were analyzed only for freight traffic specifically. Starting with the SLRTP and Freight Plan updates in 2022, general highway traffic bottlenecks were combined with freight bottlenecks within a single dataset. Prior to the 2022 plan updates, bottlenecks were ranked through an analysis of each location's value, condition, and performance (VCAP). Value was based on how much each location increased the efficiency of the highway network for trucks; condition was based on the Infrastructure Condition Evaluation (ICE) tool's analysis of condition and traffic data; and performance was based on the INRIX bottleneck ranking tool. Locations were ranked, with annual average truck traffic data being used as a tiebreaker.
Creator
Iowa Department of Transportation
Publisher
Iowa Department of Transportation
Temporal Coverage
Last Modified: 2025-08-21
Date Issued
2023-03-06
Rights
https://creativecommons.org/licenses/by/4.0
Access Rights
Public
Format
ArcGIS FeatureLayer
Language
English
Date Added
August 10, 2025
Provenance Statement
The metadata for this resource was last retrieved from IowaDOT Open Data on 2025-08-24.

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Cite and Reference

  • Citation
    Iowa Department of Transportation (2023). Scoping Bottlenecks [Iowa]. Iowa Department of Transportation. https://public-iowadot.opendata.arcgis.com/datasets/IowaDOT::scoping-bottlenecks (web service)
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