Development of Adjustment Factors for HCM Sixth Edition Freeway Work Zone Capacity Methodology TPF-5(295)

(2020) Development of Adjustment Factors for HCM Sixth Edition Freeway Work Zone Capacity Methodology TPF-5(295). Transportation, Department of

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Abstract

This project validated the Highway Capacity Manual (HCM) work zone capacity methodology for urban and rural freeways and provides recommendations for a more accurate estimation of work zone capacity. This study collected data from 16 work zone sites across Iowa in 2018 and 2019. The free flow speeds (FFSs), capacities, and queue discharge rates (QDRs) at these work zones were calculated using the HCM method and compared to field measurements. For the work zones considered in this study, the key findings are as follows:  FFSs estimated using the HCM method had a greater variance than the field-measured values. Under free flowing conditions,Iowans generally drove around the work zone speed limits, while the HCM method predicted a wide range of FFSs.  The field-measured prebreakdown capacities and QDRs were significantly lower than the values computed using the HCM method, indicating that traffic breakdown could happen at a much lower flow level than the capacity predicted by the HCM method.  With complex work zone configurations, such as narrow lanes, lane shifts, and crossovers, the observed FFS and prebreakdown capacity were significantly lower than typical work zone configurations.

Item Type: Departmental Report
Keywords: free flow speed, queue discharge rate, work zone capacity
Subjects: Transportation > Traffic Management
Transportation > Roads and highways
ID Code: 34060
Deposited By: Iowa DOT Research
Deposited On: 20 Oct 2020 20:22
Last Modified: 20 Oct 2020 20:22
URI: http://publications.iowa.gov/id/eprint/34060